10 Family Cucurbitaceae

Origin and History years (Zeven and Zhukovsky, 1975). The ancient Egyptians also cultivated cucumbers. Cucumis The cucurbits are largely tropical in origin with sativus var. hardwickii, a wild taxon native to different genera originating in Africa, tropical India, has been proposed as the wild progenitor of America, and Southeast Asia. Commercial cucur- the domesticated forms of C. sativus. Cucumbers bits are primarily herbaceous annuals that produce spread to China and Greece from India about distinctive tendril-bearing vines and are commonly 2,000 years ago (Whitaker and Davis, 1962; grown in temperate regions with long growing sea- Robinson and Decker-Walters, 1997). The Sikkim sons. Some are adapted to humid conditions while cucumber has been grown in the Himalayas as others are found in arid regions. Most are frost- food for centuries. intolerant although some species are more tolerant The cucumber also spread to Italy, and was a of low temperature than others. significant crop during the Roman Empire. In classical Rome, Pliny reported greenhouse pro- Taxonomy duction of cucumbers by the 1st century, and the Emperor Tiberius was said to have eaten them The Cucurbitaceae family is well defined but taxo- throughout the year (Sauer, 1993). Cucumbers nomically isolated from other plant families. The were probably spread to the rest of Europe by the family Cucurbitaceae consists of about 120 genera Romans. The earliest records of cucumber culti- and more than 800 species. Two subfamilies, vation appear in France by the 9th century, Great Zanonioideae and Cucurbitoideae, are well charac- Britain by the 14th century and the Caribbean at terized: the former by small, striate pollen grains and the end of the 15th century. Colonists introduced the latter by styles united into a single column. The the cucumber to North America by the mid-16th food plants all fall within the subfamily Cucurbi- century (Hedrick, 1919). Interaction between toideae and belong to two tribes: the Cucurbiteae Europeans and Native Americans spread cucum- and Sicyoideae. (Maynard and Maynard, 2000). bers throughout North America. Less than a cen- The genera Cucurbita , Cyclanthera and Sechium are tury later, European explorers observed a wide of New World origin. All other genera originated range of Native American peoples cultivating from the African or Asian tropics. In this chapter, the cucumbers along the east coast of North America production of cucumber ( Cucumis sativus ), netted from Montreal to Florida. Slaves also introduced and non-netted melons ( Cucumis melo ), watermelon cucumber directly to the Americas from Africa in (Citrullus lanatus ), and squash and pumpkin the early 1600s. By the 17th century, Native (Cucurbita spp.) will be discussed. Whitaker and Americans living in the Great Plains region were Davis (1962), Robinson and Decker-Walters (1997) also cultivating cucumbers (Wolf, 1982). and Rubatzky and Yamaguchi (1997) provide infor- mation about other crops in the family Cucurbitaceae. Botany CUCUMBER Cucumber (C. sativus) has a chromosome number Origin and History of n = 7, West Indian Gherkin ( C. anguira ), n = 12, and Armenian cucumber (C. melo), n = 12. Commercial The center of origin of cucumber is believed to be cucumber cultivars are warm-season, frost-sensi- India where it has been grown for thousands of tive annuals that are cross-pollinated by bees.

10 © Gregory E. Welbaum 2014. Vegetable Production and Practices (G.E. Welbaum)

Welbaum_Ch10.indd 10 8/4/2014 4:07:33 PM Plants commonly have a trailing or climbing Fruits can be spherical, blocky, oblong or elong- growth habit, although some bush cultivars with ated in shape and variable in size. Fruit surfaces shortened internodes also exist. Root systems are vary in the number and size of spiny warts, which extensive but shallow. Stems are square with stiff are usually more apparent on young fruit. bristle hairs, unbranched tendrils and generally Cucumber fruit are consumed immature when their range in length from 0.4 to 3 m (1.3 to 9.8 ft). flavor is mild and seeds are small and underdevel- Tendrils at each node help anchor plants and allow oped. Cucumbers are used for different purposes climbing on supports. Cucumber petioles are 3–15 cm depending on their characteristics (Fig. 10.1). (1.2–5.9 in) long. Rough leaf blades have a tri- Cultivars are often divided into the general cat- angular ovate shape from 5 to 25 cm (2.0 to 9.8 in) egories of “fresh market” or “processing” to describe wide with three- to five-angled regions or shallow- their intended uses. Cultivars grown for fresh lobed sinuses and a pointed apex (Rubatzky and market usually have a fruit length-to-width ratio of Yamaguchi, 1997). at least 4:1, dark-green color when immature, thick Cucumber plants exhibit monoecious (separate skin, slightly tapered stem and blossom ends. The male and female flowers on a plant), andromo- seed cavity of fresh market types is usually larger noecious (separate perfect and male flowers on than processing cultivars. the same plant) or gynoecious (all female) sex Cultivars developed for processing often have expression. Sex expression is genetically con- smaller vines, fruit with a length-to-width ratio of trolled but modified by the environment and about 2.5:1, bicolored pale and darker green chemicals. Application of auxin or ethephon immature color, thin skins, blocky shape and more favors both earlier and a higher percentage of prominent warts. The warts bear white or black female flowers, while gibberellin delays female loosely attached spines (spicules) in their centers. flower formation and percentages. Auxin and Fruit with white spines turn from green to white or ethephon favor female flower development while yellow at full physiological maturity when seeds gibberellin stimulates the formation of male have fully developed. The color of black-spined flowers. In monoecious cultivars, staminate flowers fruit changes from green to orange at maturity. appear first and are several times more abundant Black-spined fruit have thinner skin and lighter than pistillate flowers. Flowers occur at the fruit color compared to white-spined fruit and for nodes, staminate in clusters or singly with only many years were preferred for processing because one flower in a cluster opening at a time. Pistillate they have a more attractive appearance after pick- flowers are borne singly on the main stem and ling. However, black-spined cucumbers tend to lateral branches in monoecious types and singly prematurely develop their mature orange color at or in clusters on the main stem and lateral the stem and blossoms ends under environmental branches on gynoecious types. The large inferior stress or when over mature, so more white-spined ovary of pistillate flowers resembles a miniature cultivars have been developed for processing in fruit. Both staminate and pistillate flowers are recent years. 1–3 cm (0.4–1.2 in) in diameter with a yellow, showy five-lobed corolla. Flowers are open for a West India gherkin single day and if not adequately pollinated rap- idly abort. Small-fruited cultivars of pickling cucumbers are Flowering is influenced by photoperiod with sometimes sold as gherkins. However, the West regard to the number and sex of the flowers India or true gherkin (Cucumis anguria) belongs to formed. During short days, there is a tendency for a different species and has a different appearance earlier and more frequent pistillate flowering. Low and characteristics than C. sativus. West India temperatures may cause a similar response. gherkin is an annual, monoecious climbing vine Conversely, high temperature and long days pro- with flowers, leaves, tendrils and fruit smaller than mote male flower formation (Rubatzky and cucumber. Fruits, which are spiny, yellow, oval and Yamaguchi, 1997). High nitrogen promotes vegeta- about 5 cm (2 in) long, are eaten fresh, cooked or tive growth and inhibits flower formation. pickled. The plant may self-seed, escape from culti- Environmental stress (water, nutrient, etc.) pro- vation, and become an aggressive weed (Whitaker motes female flower formation. and Davis, 1962).

Cucurbitaceae 11

Welbaum_Ch10.indd 11 8/4/2014 4:07:34 PM Types of cucumbers Bush or vining

Parthenocarpic or pollinated

Processing Fresh market Mechanical harvest or hand pick Hand harvest (Preserved in vinegar) (sometimes used for fresh market)

Slicing 6L or 8 to 1W (Dark) Pickling 3L:1W (Light)

Greenhouse Outdoor

Black spine White spine (Orange at maturity) (White at maturity) Tender skin Regular 1. Beit Alpha 2. Burpless (Asian) 3. American Slicing

Fig. 10.1. Cucumber cultivars come in many different shapes and sizes that were developed for specific uses and markets. This figure summarizes some of the major commercial types.

Types and Cultivars dill seed) to make pickles and other products (Fig. 10.2). There are many diverse cultivars of cucumber grown Pickling cultivars have special characteristics throughout the world. Cultivars differ in their degree that make them suitable for processing in vinegar of bitterness caused by cucurbitacins that accumulate (Motes, 1975). Resistance to carpel separation and in tissues of plants in the family Cucurbitaceae. The bloating allow pickling cucumbers to retain their function of cucurbitacins is believed to be defense shape and integrity during the brining process. against herbivores. Cucurbitacins are chemically clas- Fruit are harvested for processing while immature sified as steroids but often occur as glycosides (Chen and not more than 12.5 cm (5 in) long. Cucumbers et al ., 2005). Non-bitterness in fruit is inherited as a for processing may be open-pollinated or F-1 hybrids simple recessive trait. Since plant breeders have been and are either hand or mechanically harvested, selecting against bitter flavor for many years, fruits of maturing 55–60 days from seeding. To ensure a most modern cultivars are free of bitterness. Some concentrated set for mechanical harvesting, gynoe- older heirloom cultivars may develop bitter taste, par- cious cultivars are often preferred. The first flowers ticularly when grown under environmental stress. developing on a gynoecious cultivar are female, so every flower has the potential to produce fruit Pickling resulting in a concentrated early set and uniform Immature pickling cucumber cultivars are pro- crop maturation. However, to provide a source of cessed with vinegar, spices and herbs (such as pollen, a monoecious cultivar must be added so

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Welbaum_Ch10.indd 12 8/4/2014 4:07:35 PM Plant breeding has improved the quality of the American slicing cucumber. Modern cultivars are uniformly dark green over the entire fruit with no white striped ends. The fruit shape is nearly cylin- drical with blunt ends and fruits appear circular in cross section. The pericarp (fruit) walls are thicker and the seed cavity greatly reduced. Modern culti- vars tend to have fewer warts and spines compared to older cultivars (Rubatzky and Yamaguchi, 1997). Many modern cultivars are resistant to virus dis- eases and mildew.

Parthenocarpic types Parthenocarpic slicing cultivars are also called Fig. 10.2. Pickling-type cucumber fruit at harvest seedless, English or greenhouse cucumbers. Seedless maturity. or parthenocarpic cucumbers have traditionally been grown in greenhouses to prevent bees from that 12–18% of the plants are pollinators. The introducing foreign pollen, which would cause seed male flowers of the monoecious cultivar are suffi- development (Fig. 10.4). cient to pollinate gynoecious plants (Rubatzky and Many cultvars are gynoecious, producing long, Yamaguchi, 1997). straight, smooth fruit at each axil, with thin-skins Total yields of gynoecious and monoecious culti- and medium to dark-green color. A slightly restricted vars are comparable because not all of the female “neck” at the stem end of the fruit serves to readily flowers on the gynoecious plants develop into fruit. identify this unique type. Parthenocarpic cucumber The gynoecious plant cannot produce enough fruit have a length-to-width ratio of about 6:1. The photosynthates, so some female flowers abort. skin is so thin that greenhouse cucumber cultivars Applying gibberellic acid to small plants induces are often film wrapped to protect against physical some male flower formation on gynoecious culti- damage and prevent shriveling (Rubatzky and vars for seed production. The gynoecious character Yamaguchi, 1997). may not always be stable, so some plants may be More recently, parthenocarpic cultivars have monoecious in a gynoecious cultivar. Crowding been developed for field production of both pro- may increase the percentage of monoecious plants cessing and fresh market cucumbers. Parthenocarpic in a gynoecious field depending on the stability of pickling cucumber cultivars are not dependent on the cultivar. Pickling cultivars are sometimes mar- bee pollination and produce uniform fruit for keted fresh for use in salads or fresh consumption mechanical harvest when conditions are unfavor- without pickling. able for pollination. For the processing of larger whole fruit, parthenocarpic cultivars are less desir- able because they lack seed development, which American slicing contributes to texture and flavor components asso- Fresh market cultivars popular for slicing as a ciated with quality. side dish or in salads are sometimes referred to as ‘Beit Alpha’ cucumbers were developed in Israel American types. Cultivars are usually monoecious but are gaining popularity in other parts of the F-1 hybrids that require bee pollination and mature in world as a fresh-market type. ‘Beit Alpha’, also about 80–85 days from seeding. These cultivars have known as ‘Beta Alpha’, are a type of partheno- comparatively solid dark-green skin and a length-to- carpic, all female, multi-fruited, dark-green hybrid width ratio of 5:1 or greater, 8–10 cm (3–4 in) in that do not require pollination and offer high yield diameter and 20–25 cm (8–10 in) long (Fig. 10.3). potential. The seedless fruit is 14–19 cm (5.5–7.5 in) The fruits are harvested immature well before long, with a thin smooth skin with few warts that physiological maturity, which occurs at approxi- does not need to be peeled before eating or film mately 120 days when the fruit are white or creamy wrapping to prevent postharvest dehydration. yellow in color with fully mature seeds. Fruits can be harvested when 3–4 cm (1.2–1.6 in)

Cucurbitaceae 13

Welbaum_Ch10.indd 13 8/4/2014 4:07:35 PM Fig. 10.3. Slicing cucumbers after harvest waiting to be washed and graded.

short-day conditions and many staminate flowers under long-day conditions. The Sikkim cucumber, also called the Concombre apple, is popular in India and is unique because the fruit has reddish brown skins. The Sikkim cucumber is a fat, large fruit reaching 38 cm (15 in) long and 15 cm (6 in) wide. The ripe fruit is eaten cooked, fermented or raw and has a mild flavor (Tamang et al ., 1988).

Armenian The Armenian cucumber, also called the serpent Fig. 10.4. Greenhouse-grown parthenocarpic cucumbers or snake cucumber, is a type of melon ( C. melo ) from the Netherlands. that is eaten fresh like a slicing cucumber when immature. The annual vine is creeping, with in diameter or for the specialty markets with the slender pubescent stems and rounded leaves flowers still attached. with five lobes. The sex expression is monoe- cious with small and pale yellow flowers with five petals similar to other melons. The Armenian Oriental types cucumber is long and slender with pale to dark Oriental cultivars are usually long, contain seeds, green skin that is wrinkled longitudinally without have thin dark-green skins and considerable warts spines. The slender fruit have their best flavor and spines. They are popular in Asian markets and when 25–35 cm (10–15 in) in length but if allowed are grown to a limited extent in other parts of the to grow will reach a length of about 0.9 m (3 ft) world. Oriental cultivars are often divided into two and up to 15 cm (6 in) in diameter. Fruit are groups: the day-neutral North China group and the rarely straight and often bent and twisted. The short-day South China group that is grown pri- fruit color changes to yellow when ripe with a marily for winter production. The South China mature odor similar to cantaloupe (Rubatzky group produces primarily pistillate flowers under and Yamaguchi, 1997).

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Welbaum_Ch10.indd 14 8/4/2014 4:07:36 PM Fig. 10.5. ‘Lemon’ cucumber fruit.

Novelty types (4,836,260 acres). The average world yield was 30,927 kg/ha (27,613 lb/acre) in 2011. Compared Novelty cultivars have a unique appearance that with other vegetables, cucumber occupies fourth place appeals to some consumers but generally have in importance in the world, following tomato, cole limited marketability. ‘Lemon’ or ‘Apple’ is a nov- crops and onion. In 2011 total production of cucum- elty or heirloom open-pollinated cultivar that has bers and gherkins, according to FAO, was 37.6 mil- been passed along for many generations without sig- lion metric tonne (t); Africa producing 847,737 t, nificant genetic improvement. The fruits are round, North America 1.2 million t, South America 78,570 t, have black-spines, and pale yellow-green color at the Asia 30.8 million t and Europe 3.9 million t. China immature eating stage before turning bright orange alone produced 23.6 million t. For the most current at physiological maturity when the seeds are fully information on cucumber production, please consult developed (Rubatzky and Yamaguchi, 1997; Fig. 10.5). the latest FAO Crop Production Statistics. ‘Lemon’ is andromonoecious (separate male and perfect flowers on the same plant) like cantaloupe. A hundred years ago, some botanists incorrectly Nutritional Values identified this cultivar as a cantaloupe. The seed Cucumbers are mainly water and do not contribute area is large and the pericarp wall is very thin com- a great deal to the human diet. Cucumbers are a pared to modern cucumber cultivars. good source of certain minerals like potassium but ‘White Wonder’ is a white novelty pickling are a poor source of protein, carbohydrates, fat, cucumber cultivar that lacks chlorophyll in the fruit fiber or most vitamins (Table 10.1). epidermis during immature and mature stages of development. The color is the primary characteristic that makes ‘White Wonder’ unique. The shape, tex- Production and Culture ture and flavor are similar to other pickling cultivars. Temperature requirements and crop management Economic Importance and Cucumbers are a warm-season, frost-sensitive crop Production Statistics requiring warm soil temperatures for germination Total world production of cucumbers and gher- and reliable field emergence. The minimum, optimum kins in 2011 was estimated to be 1,958,000 ha and maximum soil temperatures for germination are

Cucurbitaceae 15

Welbaum_Ch10.indd 15 8/4/2014 4:07:37 PM Table 10.1. Nutritional composition of cucumber Fertilizer and nutrition (USDA, 2011). Cucumbers respond favorably to fertilizer, so proper Nutrient Amount/100 g edible portion fertility management is a key to maximizing prod- uctivity. Fertilizer requirements vary, depending on Water (%) 96 the soil type, the environment and cultivar. There is P (mg) 17 no single recommendation that will fit all produc- Energy (Kcal) 13 Fe (mg) 0.3 tion situations. Fertilization is most efficient and Protein (g) 0.5 effective if based on preplant soil test recommenda- Na (mg) 2 tions and foliar analyses made throughout the Fat (g) 0.1 season. Most soil testing labs will rate essential K (mg) 149 minerals as being high, medium or low and recom- Carbohydrate (g) 2.9 mend how much fertilizer should be applied to suc- Ascorbic acid (mg) 4.7 cessfully grow the crop. It is important to determine Fiber (g) 0.6 how many nutrients a cucumber crop is likely to Vitamin A (mg) 45 remove during a season. The nutrients removed from Ca (mg) 14 a field by a typical cucumber crop would be 196 kg/ha (175 lb/acre) of nitrogen (N), 28 kg/ha (25 lb/acre) of phosphorus (P) and 196 kg/ha (175 lb/acre) of 60°F (15.5°C), 95°F (35°C) and 105°F (40.5°C), potassium (K) (Masabni et al ., 2011). Soil test rec- respectively. The optimum range of soil temperatures ommendation for N and K often are less than this for stand establishment is 15.5 –35°C (60–95°F) amount to account for release of nutrients for (Masabni et al ., 2011). organic matter and inputs from the nitrogen cycle. Little vine growth occurs when temperatures fall Recommendations for P additions often exceed the below 15.5°C (60°F). The growth rate increases amount removed by the crop because some P fertil- steadily as temperatures rise above 21.1°C (70°F) izer will be fixed or immobilized in soil. An adequate (Curwen et al ., 1975). Crops planted in early spring supply of micronutrients should also be provided, when soils are cool may take 8–9 weeks or more to especially for hydroponic production. reach harvest-stage, while later plantings may Nitrogen is a very important nutrient for cucumber require only 6 weeks. Under optimal conditions, production. Early in the season, adequate nitrogen pickling cultivars mature approximately 55–60 days promotes vegetative growth and canopy formation after seeding depending on the cultivar and the fruit that is needed to maximize photosynthesis to sup- size required. Slicing cultivars require an average of port later fruit development. Lower available 80 days to harvest from seeding depending on the nitrogen a little later in the season promotes flower cultivar and environmental conditions. formation and fruit set, while excessive nitrogen fer- Cucumbers should not be planted in a rotation tilization may delay flowering and reduce fruit set. after related cucurbit species like melons, squash Petiole or plant tissue analysis can be used to assess and pumpkins because of the build-up of various crop nutrient status during the growing season to insects and diseases, which live on crop residues know if adjustments in the fertility program are and are common among these related species. required. Later in the season, side dressing or fertiga- Cucumbers are very sensitive to some herbicides, so tion with nitrogen, and possibly other nutrients, may carryover from previous crops must be considered correct deficiencies and maximum yields on sandy when selecting fields for conventional production. soils, especially when crops are handpicked over an extended period. Additional nitrogen applications are Soil requirements often needed following heavy, leaching rains on light, sandy soils. Side dressing is usually not necessary for Cucumbers can be grown profitably on most fertile, crops grown for once-over mechanical harvesting well-drained soils. Loam-textured soils with organic because of the relatively short crop maturation time. matter are well suited for cucumber production. Light, sandy soils are acceptable provided they are adequately Seedbed preparation fertilized and irrigated. A pH of 6.0–7.0 is suggested for cucumbers for optimum growth. Acid soils with pH <5.5 Field production of cucumbers may be with or should be avoided (Lorenz and Maynard, 1988). without mulch. Plasticulture is the most popular

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Welbaum_Ch10.indd 16 8/4/2014 4:07:37 PM mulch and is often used in areas with short grow- on soil type, time of season and soil moisture avail- ing seasons to enhance early production of slicing ability. Many growers use precision planters and cucumbers for fresh market. Plasticulture is rarely coated seed helps deliver fungicides, biologicals or used for the production of earlier maturing pick- small amounts of fertilizer. ling cucumbers because the added cost is not war- In short season areas, cucumbers particularly for ranted and the mulch interferes with mechanical fresh market are transplanted. Transplanting may harvesting. reduce the time to first harvest by 10 days to If cucumbers are not grown on plastic, produc- 2 weeks depending on environmental conditions. tion on raised beds is recommended to improve Cucumbers are sensitive to transplant shock and drainage and to reduce belly rot of the fruit. If are best transplanted from plug transplants rather fertigation is not used, mineral nutrients should be than with bare roots. To reduce transplant shock, incorporated into the bed prior to planting. The plants should be hardened before transplanting and soil should be tilled so that it is friable and free of irrigated more frequently until plants are properly clods to provide good seed to soil contact for established. direct-seeded crops. Spacing Field establishment Spacing is dependent on cultivar, environments and There are approximately 1100 cucumber seeds/oz cultural practices. Generally recommendations for (30–35/g) (Lorenz and Maynard, 1988). Precision fresh-market cucumbers are in-row spacing of 23–31 cm planting of cucumber seeds to the right spacing and (9–12 in) with row spacing of 0.9–1.8 m (36–72 in). depth will encourage uniform emergence of seed- This results in populations of 18,000–29,600 plants/ha lings. A uniform stand will lead to concentrated (7,300–21,780 plants/acre) (Fig. 10.6). fruit set for efficient hand or mechanical har- Pickling cucumbers usually have smaller vines vesting. Precision seed spacing produces the desired than the slicer type and are grown at high popula- stand of plants, saves seed and eliminates the need tions. Depending on environmental conditions, for thinning after establishment. This is particu- maximum yields for hand-harvest may be obtained larly important for once-over destructive machine with in-row spacing of 15–31 cm (6–12 in) with harvests of pickling cucumbers. Cucumbers are 0.9–1.8 m (36–72 in) between rows. This spacing normally planted at a depth of 0.5–2 in, depending results in populations of 18,000–71,700 plants/ha

Fig. 10.6. A field of slicing cucumbers grown without plastic mulch, destined for fresh-market sale.

Cucurbitaceae 17

Welbaum_Ch10.indd 17 8/4/2014 4:07:38 PM (7,300–29,040 plants/acre). Populations of 50 plants/m 2 native bee populations are insufficient to pollinate a gave higher yields compared to lower plant popula- commercial crop. Motes (1975) recommends at least tions of pickling cucumbers (O’Sullivan, 1980). High one colony per 50,000 plants. Most cucumber flowers yields of destructively harvested pickling cucumbers are open for only 1 day and a successful pollination are obtained from plant populations of 123,500– event requires multiple bee visits. Cool wet weather 222,300 plants/ha (50,000–90,000 plants/acre) significantly reduces bee activity and pollination (Curwen et al ., 1975). These populations are resulting in low yields and/or a high percentage of mis- achieved with in-row spacing of 10–15 cm (4–6 in) shapen fruit. Pesticides that harm bees should not be with 31–71 cm (12–28 in) between rows. used and when necessary spray applications should be scheduled for late afternoon or early evening. Irrigation Greenhouse production Cucumber crops require large amounts of water. In many locations where the average rainfall during Cucumbers are important greenhouse crops in North the growing season is appreciably less than 15 in or America, western Europe and Japan. Cucumbers are erratic during the growing season, irrigation is grown during the winter in unheated greenhouses in necessary to maximize both fruit quality and yields. temperate regions. Parthenocarpic cultivars are usu- Fruits contain about 95% water. The rule of thumb ally grown in greenhouses to avoid the use of bees for at least 1 in of water per week applies to since standard field cultivars must be cross-pollinated. cucumber production. Even this amount may be Most parthenocarpic greenhouse cucumbers are insufficient to sustain growth during prolonged gynoecious F-1 hybrids. The cost of parthenocarpic drought and/or high temperatures. In areas where greenhouse cucumber seed is significantly higher than environmental stress is common, 2 in/week may be seed of standard field cultivars (Hochmuth, 2013). required. Wilting decreases yields and may reduce Plants are transplanted into a wide range of syn- fruit quality depending on the severity. The most thetic rooting media including rockwool, gravel, sand critical need for water is during the fruiting when or bagged media to avoid the buildup of disease in drought may cause “nubbing” (small fruit that are native greenhouse soils. Greenhouse soils may be ster- shriveled at one end). In crops being grown for ilized with steam or chemical fumigants. Cucumbers once-over mechanical harvest, the last irrigation may also be grafted on to special disease-resistant should be timed to allow the soil to dry sufficiently rootstocks such as Lagenaria siceraria (Molina) to allow equipment into the field. Standl. and a Cucurbita moschata (Duchesne ex. Where possible, irrigation should be applied early Pow) × C. maxima (Duchense ex. Lam.) hybrid for in the day to permit the soil and leaf surfaces to dry greenhouse production in native soils if soil fumiga- before nightfall. Prolonged periods of wet soil and tion/sterilization is not used (Hochmuth, 2013). leaves promote infection by mildew, Alternaria , Temperature control is important with an angular leaf spot, and other various fruit-rotting optimum recommended temperature of 25–28°C and foliage diseases. Overhead irrigation will pro- (77–82°F) and night temperatures of 17 –18°C hibit bee activity and should not be used in the early (63–64°F). Lower temperatures tend to favor vege- morning hours when bees are most active. tative growth while higher temperatures promote Cucumbers can be successfully irrigated by fur- flowering. High light intensities are necessary to

row, trickle and overhead sprinkler methods. obtain maximum yields. Greenhouse CO 2 levels Furrow irrigation is limited to areas where the land should be maintained between 400 and 1500 ppm is level. Surface irrigation is preferable to overhead, to maximize photosynthesis (Hochmuth, 2013). which tends to spread various diseases to the foliage and fruit. Trickle or drip irrigation is com- Harvesting and marketing monly used with plasticulture but can be used on bare soil as well. Fields of slicing cucumbers are repeatedly hand- harvested during the season. Fruit are harvested by carefully cutting or snapping fruit from the vine by Pollination hand to avoid damaging the plant. Cucumbers Bees are extremely important for field produc- develop rapidly and must be harvested every other tion of non-parthenocarpic cultivars. In most areas, day or daily under favorable growing conditions.

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Welbaum_Ch10.indd 18 8/4/2014 4:07:38 PM Delayed harvest results in excessively large fruit Diseases and inhibits the production of new fruit. Fruit are There are many diseases that affect cucumbers. carefully handled and graded after harvest. Cucumber mosaic virus, watermelon mosaic 1 poty- Cucumbers for fresh use are often individually film virus and zucchini yellow mosaic potyvirus are some wrapped or grouped in a plastic tray and wrapped to of the most important viral diseases (Zitter et al ., preserve freshness and prevent shriveling. Nontoxic 1996). The use of disease-free seed and sprayings to water-soluble wax is sometimes added to the wash control aphids may help prevent the spread of virus water to provide a thin coating on the fruit surface to diseases. Some cultivars are resistant to viruses. reduce desiccation and give fruit an attractive glossy Some of the most important fungal diseases are appearance. The parthenocarpic greenhouse slicing downy mildew (Peronospora cubensis), powdery cucumbers are usually wrapped in plastic film mildew (Erysiphe cichoracearum) and damping-off because of their very tender delicate skin that is easily (Pythium, Rhizoctonia) (Fig. 10.7). damaged. Treating seed with thiram, fungicide applications Cucumbers are generally stored at 13 –15°C to soil at planting, and spraying emergent seedlings (55–59°F) and 90–95% relative humidity (RH) and with metalaxyl controls damping-off. have a postharvest shelf life of 1–2 weeks. Like all Mildew is common on cucumber leaves, particu- cucurbits, storage at temperatures less than 13°C larly late in the season and in areas with high humidity. (55°F) causes chilling injury. Fruits injured by chill- Cultural control measures include: removing plant ing will deteriorate more rapidly when returned to debris at the end of the season to reduce overwintering room temperature and cause the formation of off- of the fungus, reducing plant populations to improve flavor. Short-term chilling before serving in salads air circulation, and avoiding excess nitrogen fertiliza- or for fresh use improves crispness. In contrast, tion. Several fungicides, such as trifloxystrobin, freezing injury will be initiated at −0.5°C (31°F). azoxystrobin and chlorothalonil + myclobutanil con- Symptoms of freezing injury include a water- trol the mildew diseases. Some cultivars are resistant soaked pulp becoming brown and gelatinous in to mildew. Biorational compounds can reduce the inci- appearance over time (Suslow and Cantwell, 2013). dence of powdery mildew on cucurbits. Biorational Cucumbers are highly sensitive to exogenous materials include natural and mineral oils, peroxi- ethylene. Accelerated yellowing and decay will gens, cow’s milk, silicon, and salts of monovalent result from low levels (1–5 ppm) of ethylene during cations such as sodium, potassium and ammonium distribution and short-term storage. Do not mix (Bélanger and Labbe, 2002). commodities such as bananas, melons and toma- Stripped and spotted cucumber beetles transmit bac- toes with cucumber (Suslow and Cantwell, 2013). terial ( Erwinia tracheiphila ) wilt among plants during Controlled or modified atmosphere storage and/ feeding. Cucumber beetle feeding does little direct or shipping offer moderate to little benefit for damage to plants but the bacteria introduced during maintaining cucumber quality. Low O levels 2 feeding proliferate in the xylem reducing water flow (3–5%) delay yellowing and the onset of decay for between the roots to leaves. Bacterial wilt sympto ms a few days. Cucumber tolerates elevated CO 2 up to 10% in controlled atmosphere storage but storage life is not extended beyond the benefit of reduced

levels of O2 (Suslow and Cantwell, 2013). Pickling cucumbers may also be repeatedly hand- harvested but the trend has been toward greater use of once-over destructive mechanical har- vesting, particularly for processing, to cut labor costs. A mechanical harvester cuts the vines at the soil surface and conveys the plants up a conveyer to a set of rollers that pinch the fruit from the vine as the plants are fed between the rollers. The vines and immature fruit are returned to the field and fruit of the desired size are conveyed to an adjacent vehicle or wagon and taken to the processing facility for washing, grading and processing. Fig. 10.7. Cucumber leaf with powdery mildew infection.

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Welbaum_Ch10.indd 19 8/4/2014 4:07:38 PM are similar to drought stress and in severe cases will kill Modern-day cultivars share main characteristics of plants. Some cucumber cultivars are more resistant to earlier cultivars but greatly improved for uniformity, bacterial wilt than others. Other cucumber pathogens size, shape, flesh thickness, sugar content and quality. include: angular leaf spot ( Pseudomonas syringae pv. ‘Netted Gem’ introduced by W. Atlee Burpee Seed Lachrymans ), gummy stem blight ( Didymella bryo- Company from France in about 1880 made an niae ), common anthracnose ( Colletotrichum spp.), important contribution to cultivar development in fruit wet-rot ( Choanephora cucurbitarum ), Fusarium North America. Shipping and storage characteristics wilt, Cladosporium scab and bacterial soft rot ( Erwinia were of no importance until after 1900. Today spp.) (Zitter et al ., 1996). Cucumber growers should melons are most commonly eaten fresh, as a salad or consult local recommendations for tested and approved as a dessert (Rubatzky and Yamaguchi, 1997). control measures as well as disease-resistant cultivars. Botany and Life Cycle Insect Pests Melon is a general term for fruit produced by various Some of the most troublesome insects of cucumber members of the family Cucurbitaceae. In some areas include cucumber beetles ( Diabrotica and the term is applied to both netted and non-netted Acalymma spp., vector of bacterial wilt), Epilachna members of C. melo but not watermelon. In other spp. beetles, greasy worm ( Agrotis ipsilon ), the regions of the world, the terms cantaloupe and/ melon fruit fly ( Dacus spp.) and aphids. These pests or muskmelon are used to describe the netted melon can be controlled with insecticides. Control with while other types of C. melo are called “melon”, natural enemies is highly developed in greenhouses “mixed melon” or sometimes “winter melon”. Cucumber but less so for field cultivation. Please consult local and melon are both members of the genus Cucumis recommendations for effective control measures. but different species, so they do not cross-pollinate. Since cucumber and melons are related, some of the information on cucumber also applies to melon. NETTED AND MIXED MELONS Naudin classified different forms of C. melo into separate botanical varieties in 1859. Although Origin and History Naudin’s classification was not recognized taxo- Netted melons, also called muskmelons or canta- nomically, it was useful for many years to delineate loupes, appear indigenous to Africa (Zeven and obvious horticultural differences among fruit types Zhukovsky, 1975). The oldest record appears to within C. melo. Many of the botanical variety des- come from Egypt were muskmelon cultivation ignations are now classified into eight horticultural occurred as early as 2400 bc . Netted melons were groups under C. melo (Table 10.2; Rubatzky and known to Greeks about 300 bc . Truly wild forms are Yamaguchi, 1997). found only in eastern tropical sub-Saharan Africa. The related wild forms reported in India are likely undomesticated escapes derived from local cultivars. Table 10.2. Groups of Cucumis melo (Rubatzky and Once domesticated, melon diversity expanded into Yamaguchi, 1997). numerous cultivars, especially in India, which is con- sidered a secondary center of origin (Zeven and Group name Common name/characteristics Zhukovsky, 1975). Cultivars were rapidly dispersed Cantaloupensis Netted melons (muskmelon and throughout Europe and fairly early into the Americas. (formerly cantaloupe) as well as lightly or Columbus reportedly carried seed to the New World Reticulatus) non-netted cultivars. Perishable in 1494 and the Spaniards introduced melons into Inodorus Winter melons or mixed melons. Some the Americas in the late 1500s. North American may be stored for several weeks natives were growing muskmelons during the 1660s Flexuous Armenian cucumber, snake or (Rubatzky and Yamaguchi, 1997). serpent melons The term muskmelon is derived from musk, which Comonon Oriental pickling melon is a Persian word for a kind of perfume. The name Chito Mango melon or vine peach melon cantaloupe is believed to have arisen from the city of Dudaim Queen Anne’s pocket melon Momordica Snap melon Cantaluppi in Italy or from the estate and castle of Agrestis Wild types Cantalupo also in Italy (Rubatzky and Yamaguchi, 1997).

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Welbaum_Ch10.indd 20 8/4/2014 4:07:38 PM Fruit size and characteristics vary widely among have longer storage life than the Cantaloupensis groups and cultivars (Table 10.2). Fruit shape varies group. One exception to this description is the from spherical to oblong. Many fruits are covered ‘Crenshaw’ melon, which has a short shelf-life and with corky reticulate netting while others are can be very odoriferous. Winter melons generally smooth. The vein tracts or sutures are longitudinal require a growing season that is several weeks indentations or stripes on the fruit surface associ- longer than most members of the Cantaloupensis ated with vascular bundles, which may not be vis- Group. Best fruit quality is obtained at high temper- ible in fruits that are heavily netted. The edible atures from 30 to 35°C (86–95°F) in semi-arid melon flesh is actually the fruit pericarp, which environments with low humidity. varies in thickness, color and texture. Pericarp ‘Honeydew’ fruit have pale green rinds that colors maybe white, green, pink or orange. Aroma turn creamy white when mature (Fig. 10.8). The varies from strong to odorless and depends on the firm, thick, juicy flesh is pale green to white at quantity and quality of volatile compounds pro- maturity. Fruit do not abscise when ripe so judg- duced. Melon fruits produce from 300 to 500 seeds ing maturity can be more difficult than for netted each arising from separate fertilization events. The melons that slip. ‘Honeydew’ fruit have moderate seeds are smooth, range from 5 to 15 mm in length storage life of up to several weeks under the right and have yellow or beige coloration. On average conditions. Honeydew can accumulate high sugar there are approximately 30 seeds/g. contents and when fully ripe may have a soluble solids content in excess of 16%, among the high- est of any melon. ‘Honeydew’ was selected from Types and Cultivars the French cultivar ‘White Antibes’ in the state of This section focuses on the most widespread and Colorado in the USA (Rubatzky and Yamaguchi, economically important Groups Cantaloupensis 1997). and Indorous. Cultivars in the Inodorous and ‘Crenshaw’ originated by chance in a musk- Cantaloupensis Groups can be intercrossed. The melon field (Rubatzky and Yamaguchi, 1997). The Group Inodorus contains the so called “winter ‘Crenshaw’ fruit is smooth and oblong with some melons” such as ‘Casaba’, ‘Canary’, ‘Honeydew’, ribbing at the tapered stem end (Fig. 10.9). ‘Crenshaw’ ‘Honeyloupe’, ‘Crenshaw’, ‘Canary’ and ‘Santa fruit exhibit intermediate stem abscission, are very Claus’ that do not abscise from the vine at maturity, susceptible to sunburn, and have poor shipping and lack heavy netting, are generally less aromatic, and storage qualities. The immature fruit rind is dark green.

Fig. 10.8. ‘Honeydew’ fruit in a California production field.

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Welbaum_Ch10.indd 21 8/4/2014 4:07:39 PM Rind color change is not uniform and ripe fruit are well adapted to shipping and can be stored for often have sections of both green and pale yellow. several weeks. The ripe fruit have moderately firm, salmon-colored ‘Santa Claus’ is an oblong slightly warted melon flesh with a mild perfume-like aroma. The flesh is with a hard rind that is green and yellow, vaguely sweet with 12–14% soluble solids (Rubatzky and striped, and has little aroma. The flesh is firm and Yamaguchi, 1997). whitish green with a soluble solids content of ‘Casaba’ fruit have a greenish yellow, thick, 6–8%. The fruit are suitable for shipping and relatively hard rind with shallow ribs and no net- under cool temperatures can be stored for approxi- ting. Fruits are round but tapered at the stem end mately 3 months if the rind is not damaged. (Fig. 10.10). The white flesh is moderately firm The netted fruit of group Cantaloupensis (for- with an aroma reminiscent of cucumber. The fruit merly Reticulatus) are called muskmelon and/or do not abscise at maturity and have a long storage cantaloupe in many markets. A unique feature of life of up to a couple of months at cool temperat- some muskmelon/cantaloupe cultivars is that they ures. The flesh has a soluble solids content of 6–8%. detach from the vine at maturity in a series of ‘Juan Canary’ fruit are oblong, smooth, and stages known as “slip”. The slip stages are useful intense yellow. The flesh has little aroma and is for characterizing maturity. Fruits progress from whitish green. The flesh has a soluble solids con- complete stem attachment to ¼, ½, ¾ and finally tent of 6–8%. The fruit do not abscise at maturity, full slip during ripening, becoming increasingly aromatic and yellowish orange in color (Fig. 10.11; Rubatzky and Yamaguchi, 1997). The name cantaloupe is often associated with fruit produced in North and Central America in arid regions with low humidity and high temperat- ures. Cantaloupe fruit characteristics are desirable for long-distance shipping and include: round and small shape, weight of approximately 1.5–2 kg (3.3–4.5 lb), uniform heavy netting, indistinct rib- bing, firm thick flesh and small, relatively dry seed cavity (Fig. 10.12). In contrast, muskmelon cultivars grown for local markets in the eastern USA and Canada are adapted for production under humid conditions, have spherical or elongated fruit shape, prominent Fig. 10.9. ‘Crenshaw’ fruit in a California field. The yellow fruit on the left is ripe and the green fruit is immature. The vein tracts and ribbing, larger size (2.3–3.6 kg; 5–8 lb), rind is very sensitive to sunburn and fruits not protected strong flesh, strong aroma, large moist seed cav- by the canopy are sometimes protected with bags. ities, and relatively soft flesh. Most muskmelons have relative poor shipping and storage character- istics and are better adapted to local or regional markets (Fig. 10.13). Many modern muskmelon cultivars developed for the eastern USA and Canada have incorporated the beneficial fruit characteristics of western canta- loupes to improve shipping and storage life but with larger fruit size and tolerance of high humidity. This trend has blurred the distinction between muskmelon and cantaloupe cultivars. Today, older large-fruited aromatic muskmelon cultivars are popular in some markets as heirlooms. Melon retailers are making a conscious effort to eliminate the word “muskmelon” from marketing because of Fig. 10.10. Mature bright yellow ‘Casaba’ fruit in a the negative connotations associated with the term California production field. “musk” and the strong aromas the name implies.

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Welbaum_Ch10.indd 22 8/4/2014 4:07:40 PM (a) (b) (c) (d)

Fig. 10.11. Cantaloupe fruit naturally separate from the vine in a series of stages described by the percentage of stem attachment. Before the fruit begins to ripen, the stem is securely attached to the fruit (a). As ripening commences, the stem begins to separate so that when ¼ of the stem is free of the fruit it is often called ¼ slip stage (b), half separation is ½ slip (c) and total separation is full slip (d).

Plant characteristics Commercial cultivars of C. melo types are warm- season, frost-sensitive annuals that are cross-pollin- ated by bees. Sex expression is andromonoecious or sometimes monoecious. Commercial cultivars are day-neutral. Plant habit is vining with varied inter- node length. Bush cultivars have been developed for some types. Many cultivars have tendrils at each node and flowers have five yellow petals that are open for a single day, like cucumber. However, leaves differ from cucumber in being circular, oval or kidney shaped with five to seven rounded lobes. Many com- mercial cultivars are F-1 hybrids. The main advan- Fig. 10.12. A western shipping-type melon commonly tages of F-1 hybrids are uniformity and hybrid vigor. grown in California, Arizona, Texas, Mexico or Central America for distant markets. Most commercial cultivars are andromonoecious so F-1 hybrid seed production requires emasculation of the hermaphrodite flowers and cross-pollination by Increasingly the word cantaloupe is used exclu- hand. Manual labor increases the cost of hybrid seed sively for marketing netted melons in the USA. by several times compared to open-pollinated. It is Not all netted melons abscise at maturity. Some estimated that at least 80% of the netted melons Japanese cultivars have netting and vein tracts like grown in the USA are F-1 hybrids. A lower per- western cantaloupe cultivars but ripen without centage of winter melon cultivars are F-1 hybrids. abscission like members of the Inodorus Group. Fruit of these cultivars are often sold with stems Production and Culture attached to the fruit in a T configuration (Fig. 10.14). Persian melon cultivars produce large-round net- According to FAO, in 2011 the total annual world ted fruit that resemble western shipping-type canta- production of melons was about 25.5 million t loupes. Persian fruit do not detach at maturity and from 1,008,700 ha. Major melon-producing coun- are usually classified in the Inodorus Group despite tries were China (12.2 million t), followed by their shallow netting, mild aroma, small moist seed Turkey (1.7 million t), Iran (1.2 million t), the USA cavity and firm salmon-colored flesh. Persian (1.1 million t) and Spain (1.0 million t). In the USA, melons can be crossed with other Cantaloupensis California was the leading producer of all melons, types to create melons with good shipping charac- accounting for 33% of total acreage in 2005, fol- teristics and longer shelf life. lowed by Texas, Georgia and Arizona. By acreage Cultivars of other Cantaloupensis melons have and weight, California leads the USA in cantaloupe either sparse netting or lack netting entirely but and honeydew production. have vein tracts and thin rinds. Examples include In the past, melons were considered “seasonal delights” ‘Charentais’, ‘Ananas’, ‘Ha-ogen’ and ‘Valencia’. because of their limited availability throughout the year.

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Welbaum_Ch10.indd 23 8/4/2014 4:07:42 PM Fig. 10.13. A classic muskmelon cultivar traditionally grown for local markets in the eastern USA and now as heirlooms.

Fig. 10.14. Japanese melons grown in tunnels early in the season and then uncovered later so the structure supports vine growth. These fruit resemble cantaloupe but do not abscise at maturity and have characteristics similar to the Winter Melon Group (Table 10.2).

Production for export has developed in Medi- mixed melons in the world. Many of the US terranean countries, Australia, Costa Rica, Guatemala, imports come from Costa Rica and Guatemala. Taiwan and Japan, using F-1 hybrid cultivars with France and the UK are also large import markets improved shelf life. Today, not only is the USA a for melons. In tropical Asia, melons are more of a net importer of melons (imports minus exports) luxury crop for urban markets, grown in the drier but it is the largest importer of cantaloupes and lowlands and highlands.

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Welbaum_Ch10.indd 24 8/4/2014 4:07:44 PM Site selection raised bed. After planting, the trench is covered with clear plastic and secured at the edges with soil. Melons grow well in a wide range of fertile and well- The plastic cover is cut open or removed entirely drained soils. Maximum yields are achieved on when the melon plants begin to vine and tempera- medium-textured soils with high water-holding cap- ture control is no longer required. The plastic cover acity and good internal drainage. Peat and heavy clay protects from fly-in insects while intact. soils should be avoided because their poor aeration and restricted drainage inhibit root growth and fruit quality. Melons are sensitive to saline and acid soils Low row covers but will grow well on slightly acidic (pH 6.8) to mod- Plastic tunnels are suspended over melon beds by erately alkaline (pH 8.0) conditions. tightly stretching clear plastic film over wire hoops A crop rotation cycle of several years without for temperature modification in short-season areas. growing other members of the family Cucurbitaceae Row covers can be used longer in the season than (cucumber, pumpkin, watermelon, etc.) is recom- with trenches but are more expensive and may mended if pathogen populations are high and fumi- require ventilation on sunny days. Beds under clear gation is not used. When possible, grasses, corn or plastic tunnels may be covered with plastic mulch sorghum are good rotation crops. Carryover from to provide weed control and to conserve water. herbicides, such as atrazine (2-chloro-4-(ethylamino)- 6-(isopropylamino)-s-triazine), may inhibit melon growth. Fertilizer and nutrition Seedbed preparation Melons develop extensive root systems that effi- In many regions, melons are generally grown on ciently explore the soil for water and available raised beds 15–20 cm (6–8 in) high. Final spacing of nutrients. For this reason, fertilizer requirements the beds in furrow-irrigated culture is generally 203 cm are moderate compared with many other vegetable (80 in) center-to-center. Beds can be created and crops. An effective nutrient management program shaped to final spacing before planting or to one- provides sufficient quantities of N, P, K, S, Ca, Mg, half final spacing (102 cm; 40 in). In the latter pro- B, Cu, Fe, Mn, Mo and Zn so that plants develop cedure, every other bed is seeded at planting. When and maintain a large canopy of healthy leaves plants begin to vine, unplanted beds are broken throughout the season. Fertilizer should be applied open and the field is reworked to position the plant in accordance with both soil and foliar test results row in the middle of the final 203 cm (80 in) bed. when possible. Nitrogen is the most commonly required fertilizer, although P is sometimes needed to promote good seedling vigor, maximum prod- Plastic mulch uctivity and high fruit quality, especially in alkaline In short-season areas, plastic mulches heat cold soil soils. Mineral soils may contain adequate K but to stimulate early season growth. In other areas, losses through leaching necessitate annual add- mulch is popular for fumigation, moisture conserva- itions, especially in areas with light soils. The tion, reducing fruit rot, preventing the leaching of approximate absorption of N-P-K by a melon crop nutrients following heavy rains, and providing weed is 174 kg/ha (155 lb/acre), 28 kg/ha (25 lb/acre) control. Plastic film is installed over a 203 cm (80 in) and 174 kg/ha (155 lb/acre), respectively. Soil test bed and secured at the edges with soil. Planting is by recommendation for N and K often are less than direct seeding or transplanting through holes these amounts to account for nutrient release for punched or burned in the mulch. Water is applied organic matter and inputs from the nitrogen cycle. under the plastic by drip irrigation or fertigation. Recommendations for P additions often exceed the amount removed a melon crop because some P fer- Trenches tilizer will be fixed or immobilized by certain soil types (Lorenz and Maynard, 1988). For early-season plantings in some areas, seeds are For conventional production, granular phosphorus planted in the bottom or on the north slope of a fertilizer may be applied preplant, as 10-34-0 or plastic-covered trench dug approximately 46 cm 0-52-0 for example, in twin bands 15 cm (6 in) deep (18 in) wide and 15–20 cm (6–8 in) deep in the and 10–15 cm (4–6 in) to either side of the planted center of a standard east-west, 203 cm (80 in) row or in drip irrigation lines as part of a fertigation

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Welbaum_Ch10.indd 25 8/4/2014 4:07:44 PM program. Phosphorus can also be banded and lightly temperatures are below 21°C (70°F) have poorer incorporated before beds are formed, but alkaline quality. Melons grow best in hot weather but very mineral soils chemically tie up phosphorus, making it high temperatures (43–46°C/110–115°F) may cause unavailable to the plants. Thus, banding the fertilizer temporary vine wilting and softer ripe fruit with near the seed is preferred over broadcast application reduced shelf life (Lorenz and Maynard, 1988). (Lorenz and Maynard, 1988). Melons are often planted in single rows spaced Nitrogen is often applied in two side-dressings or 203 cm (80 in) apart (Fig. 10.15). Seeds are planted through fertigation, the first at the two- to four-leaf from 1.25 cm (0.5 in) to 2.5 cm (1.0 in) deep. stage and the second at vine proliferation. Melon leaf In-row spacings of 7.5–15 cm (3–6 in) are common. petiole tissue analysis provides an effective diagnosis After plants reach the two- to four-leaf stage, they of crop nutrient status and allows continuous moni- are sometimes thinned to an in-row spacing of toring of crop fertility throughout the season so approximately 20 cm (8 in) for a final stand of about inputs can be applied only if required to maximize 4,000 plants/ha (10,000 plants/acre). In some areas fruit yields and quality. Over-fertilization, especially on small plots, melons are planted in hills 1.3–1.8 m with N, favors vegetative growth over reproductive (4–6 ft) apart with three or four seeds per hill growth and may inhibit fruit set. The N level, espe- (Lorenz and Maynard, 1988). cially ammoniacal N, must be relatively low at Vacuum planters optimize use of expensive hybrid flowering to encourage fruit set and development seed by precision placement. Under ideal conditions, over the production of new leaves and vines. Moderate seeds are planted to a final stand at 15–20 cm (6–8 in) N tissue levels favor sugar accumulation in the fruit spacing and not thinned (Table 10.3). rather than additional vegetative development. Narrow spacing reduces fruit size while wider spacing increases it. Hybrids usually are less affected by close spacing than open-pollinated cultivars. Field establishment Melon seeds are often film coated. Film coating The minimum, optimum and maximum soil tem- offers several advantages, such as less abrasion and peratures for seed germination are 16°, 35° and 38°C clogging of planter parts, easier cleanup and main- (60°, 95° and 100°F), respectively. Germination is tenance of equipment, addition of fungicide or slow and erratic when soil temperature is below small quantities of fertilizer to seeds, and checking 20°C (68°F). Fruit maturing when daily mean air of seed placement in soil.

Fig. 10.15. Cantaloupe field on raised beds in the Central Valley of California during harvest season.

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Welbaum_Ch10.indd 26 8/4/2014 4:07:45 PM Table 10.3. Number of seeds needed to plant 0.4 ha but this may increase foliar and fruit disease in (1 acre) when rows are spaced 203 cm (80 in) apart mature plants. (Lorenz and Maynard, 1988). Furrow irrigation is a relatively inefficient method that is still used in some flat desert areas. When In-row spacing cm (in) Seeds/ha (seeds/acre) using furrow irrigation, care must be taken to ensure 5 (3) 26,150 (10,460) that water reaches the seed or root zone, and that 10 (4) 19,600 (7,840) after vines start to run, the top of the bed does not 15 (6) 13,050 (5,220) become wet and encourage fruit rot. Poor drainage, 20 (8) 9,800 (3,920) flooding or standing irrigation water may damage 25 (10) 7,850 (3,140) melon crops. Common problems associated with excessive water are weak root systems that may lead Transplants are used primarily in areas with to vine collapse as the crop reaches maturity, poor short growing seasons to reduce development time. fruit netting and low fruit sugar content. Melons do not easily produce adventitious roots and are considered difficult to transplant, espe- Flowering and pollination cially with bare roots. Melons are most easily transplanted from plug trays with soil around the Melon sex expression is most commonly andromo- roots. Transplants are grown in protective struc- noecious because separate male and perfect flowers tures until they have two to four true leaves and occur on the same plant. Both male and perfect flowers conditions are sufficiently warm for rapid field are open for only 1 day. Male flowers rapidly sen- growth. Prior to field planting, transplants should esce and dehisce after closing, but fruiting flowers be hardened to increase dry matter and stress toler- often remain attached for several days. If pollination ance by withholding water, mechanical condi- is successful, the ovary rapidly enlarges and “set” tioning or exposure to suboptimal temperatures. fruit, while the remaining fruiting flowers senesce and Plants should be kept well watered to minimize abscise. Most vines only support a few developing fruit stress after field planting. A liquid fertilizer or at once and most later fruiting flowers will not set. “starter” solution is often applied to the root zone Melon pollen is sticky and must be transferred at transplanting to encourage rapid growth. from stamens to the pistil by insects. The most effective pollinators are bees. Several hundred pollen grains must be uniformly transferred to each lobe of Irrigation the stigma of each fruiting flower. Poor or inadequate Muskmelon have extensive, moderately deep, root pollination of each lobe will result in misshapen and/ systems that efficiently remove water from soil, so or small fruit. Adequate pollination requires 10–15 irrigations may be less frequent than with some bee visits during the single day a flower is open. The other vegetables. However, the general recommen- grower and beekeeper must time colony placement dation for at least 2.5 cm (1 in) of water per week with the start of flowering. If colonies are placed pre- still applies particularly during pollination and rapid maturely before flowering, bees will migrate to fruit development. Post-plant irrigations ensure seed another source of pollen and will not work the germination, emergence and stand establishment. intended field. Conversely, if bees are placed in the However, when possible, irrigation may be withheld field too late, the first flowers will not be pollinated. or carefully managed until the pre-vining stage to One or two strong colonies per acre are required to avoid cooling the soil, to discourage damping-off ensure sufficient bee visits to adequately pollinate a diseases and to encourage deep rooting. The final melon field and maximize yield and quality. irrigation is typically 7–10 days prior to harvest, but Bee colonies are often placed around the per- may vary depending on environmental factors such iphery of the field, but placement within a field as soil type, air temperature and humidity. may increase the frequency of flower visits with the Drip irrigation, either with or without plastic same number of colonies. Communication between mulch, is common in the eastern and increasingly the grower and beekeeper is essential to minimize the western USA as well as other areas where irri- bee kill if harmful chemicals are used and colony gation is required. Drip conserves water and pro- disruption by cultural practices. vides uniform application to the root zone. Melon Environmental and disease factors may signifi- fields are often established with sprinkler irrigation cantly influence flowering, pollination and fruit set.

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Welbaum_Ch10.indd 27 8/4/2014 4:07:45 PM Plants under stress will have fewer flowers and will photosynthetic capacity; and unfavorable growing not set as many fruit as healthy plants. Rain, fog, conditions such as extreme temperatures, high strong winds and extreme temperatures will reduce humidity, excess moisture or competition from weeds. bee activity and consequently yields. When selecting a fruit, consumers should avoid “slick” cantaloupes with poor netting. These are considered off-types because they have an abnormal appearance. Fruit quality The best quality cantaloupe fruit are true-to-type with Soluble solids (sugars) accumulation depends upon heavy netting, uniform shape and good size. the plant’s ability to produce sufficient quantities of Fruit color is more stable under environmental sugars by photosynthesis to meet metabolic needs changes than soluble solids, especially when stress plus excess for fruit storage. For high fruit sugar occurs close to harvest. However, color intensity is content, it is important to have a large leaf canopy decreased by plant stress during the earlier stages of prior to fruit set to maximize photosynthesis and fruit development. Disease, poor nutrition, water- support fruit growth. Any factor that limits photo- logged root systems, extensive insect or mechanical synthesis will also decrease sugar accumulation in damage and strong weed competition (shading) reduce fruit. Factors that limit fruit sugar content include: color. Interestingly, mild water stress, as might be reduced leaf area (leaf size and number, disease, present under semi-desert or desert conditions, seems insects, mechanical damage); reduced photosyn- to enhance fruit flesh color intensity (Rubatzky and thesis (insufficient leaf area due to viral infection, Yamaguchi, 1997). foliage disease, insect damage, mechanical damage, Flesh thickness is largely genetically controlled chemical damage or air pollutants such as nitrogen and is one of the most stable fruit quality charac- oxides or ozone, cloudy weather, dust, shading by teristics. Fruit cavity size is a factor in shipping and other plants, opaque sprays); water stress (dry soil, holding ability of fruit. Fruit with a small tight restricted root growth); and competing needs for cavity ships better. Rough handling of fruit, espe- sugar compounds within the plant (vegetative cially throwing, causes loose seed cavities, some- growth, repair of damaged tissue, combating dis- times caused “shakers” because of the sound the ease). The highest melon sugar content is produced dislodged seeds make when the fruit is rapidly during warm sunny days and cool clear nights when moved back and forth. Large cavities may result in plants are not diseased or stressed. Sugar content of softer fruit that does not ship or hold as well as melons are easily measured by expressing a few drop fruit with a small solid seed cavity. of fruit juice on to a refractometer. By some stand- ards, 9% soluble solids, reported as °Brix, is the Harvesting and marketing minimum industry standard allowed for shipment to preserve quality and reputation. Soluble solids of The time to harvest netted melons is easily deter- 9% are needed to achieve a grade of USA No.1, and mined because the vine and the fruit naturally sep- USA Fancy Grade requires 11% along with other arate or “slip” as ripening progresses (Fig. 10.11). criteria. A good tasting netted melon contains about For local markets, netted melons are harvested at 14% soluble solids (Suslow et al ., 2013). 1/4 or 1/2 “slip”. In other words, the fruit is har- Besides sugar accumulation, other characteristics vested when the stem is only 1/4 or 1/2 attached to associated with cantaloupe fruit quality are netting, the fruit. This varies somewhat because certain flesh color, flesh thickness, flesh texture, aroma and cultivars are riper at a particular slip stage than cavity size. During netted fruit enlargement, certain others (Suslow et al ., 2013). cells in the fruit epidermis divide to form a layer of For distant markets, melons are sometimes har- corky tissue under the fruit surface. This corky tissue vested preslip, which is before full maturity. eventually protrudes through fissures on the rind sur- Consumers should avoid buying cantaloupe fruit face that forms the fruit net. Favorable temperatures, with the stems still attached because they usually plant nutrition and moisture as well as freedom from have lower sugar content and crunchy texture due disease, insects or other stresses help produce a rugged to premature harvest. A “wet nose” (moist stem attractive net that also protects the fruit from abrasion end of the fruit) is a good indication that the fruit during shipment. Examples of stress conditions that was recently harvested. reduce net formation are: insufficient or excess nutri- Optimum harvest is more difficult to determine for ents or moisture; poor root development; reduced melons that do not “slip” from the vine at maturity.

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Welbaum_Ch10.indd 28 8/4/2014 4:07:45 PM For example, honeydew fruit are often harvested as they Diseases reach mature size. The plant hormone ethylene is some- There are a number of important diseases that affect times applied to ripen honeydew after harvest. Ethylene melons. Growing resistant cultivars effectively prevents is a natural gaseous plant hormone that triggers ripening Fusarium wilt ( Fusarium oxysporum f.sp. melonis ) in many fruit including both netted and winter melons. (races 0, 1, 2 and 1-2). Powdery mildew ( Sphaerotheca Rates of ethylene production vary from 40 to 80 µl/kg/h fuliginea and Erysiphe cichoracearum ) is controlled at 20°C (68°F) for intact fruit and 7–10 µl/kg/h at by fungicide applications, but modern F-1 hybrids are 5°C (41°F) for fresh cut fruit (Suslow et al ., 2013). tolerant of most races. Downy mildew ( Peronospora Fruits that are signaled to ripen by ethylene are cubensis ) is important in hot and humid climates and called climacteric. The climacteric response includes is controlled by fungicides. Gummy stem blight increased fruit respiration, fruit softening, a change (Didymella bryoniae ) is also a disease in humid and immature to mature fruit color, and increased aroma. hot conditions. Seed treatment, crop rotation and fun- In the USA, cantaloupes with altered ethylene response gicides control anthracnose ( Glomerella cingulata ). have been genetically engineered to ripen more slowly Damping-off ( Pythium sp. and Rhizoctonia sp.) is to prolong shelf life and decrease storage losses. These prevented by treating seed with fungicides, such as cultivars were tested but never brought to market. thiram. Bacterial wilt ( Erwinia tracheiphila ) causes Controlled atmosphere storage or shipping offer symptoms similar to drought stress because bacteria only moderate benefits for cantaloupes under clog the xylem, reducing the flow of water through the most conditions. With extended transit times of plant. Bacterial wilt is controlled by removing 14–21 days, cantaloupes are reported to benefit from affected plants and by controlling the striped and delayed ripening, reduced respiration and associ- spotted cucumber beetles, which vector the bacteria ated sugar loss, and inhibition of surface molds and (Fig. 10.16). decay. Modified atmospheres of 3% O and 10% 2 Other diseases include: angular leaf spot CO at 3°C (37.4°F) are effective. Elevated CO at 2 2 (Pseudomonas syringae pv. lachrymans ), Cercospora 10–20% is tolerated but will cause effervescence in leaf spot ( Cercospora citrullina ), Alternaria leaf spot the fruit flesh. This carbonated flavor is lost on (Alternaria cucumerina ) and scab ( Cladosporium cucu- transfer to air. Low O (<1%) or high CO (>20%) 2 2 merinum ) fruit and foliage disease (Zitter et al ., 1996). will cause impaired ripening, off-flavors and odors Cucumber mosaic virus cucumovirus, water- and other condition defects (Suslow et al ., 2013). melon mosaic 2 potyvirus and zucchini yellow mosaic potyvirus all affect melon and are trans- Postharvest cooling mitted by aphids, in particular Aphis gossypii. Sources of resistance to these three viruses and also Postharvest cooling is very important to maintain fruit quality by slowing the rate of fruit respiration and ripening after harvest. In some areas, melons are harvested at night or in the early morning when fruit temperatures are naturally low to reduce field heat. After harvest, melons are forced-air cooled to 50–55°F (10–13°C) but no lower since they are chilling sensitive. Because melons, and particularly netted melons, can harbor harmful bacteria in the corky tissues of the rind, melon fruit should be washed thoroughly before cutting. This is especially important for crops produced using animal manures, which can be a source of biological contamination along with poor worker sanitation. Fruit should be stored for less than 3 days after cutting to reduce the risk from Salmonella or other bacterial pathogens. A chlorinated postharvest dip treatment can provide some control of fruit rot diseases as well as human pathogens such as Listeria, E. coli and Salmonella. Fig. 10.16. Bacterial wilt of cantaloupe.

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Welbaum_Ch10.indd 29 8/4/2014 4:07:46 PM to the vector A. gossypii are available. Other virus Table 10.4. Nutritional composition of netted melons diseases in melon are papaya ringspot potyvirus (USDA, 2011). (aphid transmitted), melon necrotic spot carmovi- Amount/100 g edible rus (transmitted by the soil fungus Olpidium sp.) Nutritional value portion and beet curly top hybrigeminivirus (BCTV) (trans- mitted by leafhoppers) (Zitter et al ., 1996). Energy 141 kJ (34 kcal) Carbohydrates 8.16 g – Sugars 7.86 g Insect Pests – Dietary fiber 0.9 g Pests in melon are thrips ( Thrips palmi and Fat 0.19 g Frankliniella spp.), spider mite ( Tetranychus urticae ), Protein 1.84 g Water 90.15 g melon aphids ( Aphis gossypii ), melon fruit fly Vitamin A equivalent 169 µg (21%) (Bactrocera cucurbitae ), cucumber beetles ( Diabrotica – β-carotene 2020 µg (19%) spp.), leaf folder ( Diaphania indica ) and the leaf feeder Thiamine (vitamin B1) 0.041 mg (4%) (Aulacophora indica ). Root knot nematodes ( Meloidogyne Riboflavin (vitamin B2) 0.019 mg (2%) spp.) can be a serious problem when melons are grown Niacin (vitamin B3) 0.734 mg (5%) without proper crop rotation. Control by wide-spec trum Pantothenic acid (vitamin B5) 0.105 mg (2%) soil fumigants can be effective, but these are expensive Vitamin B6 0.072 mg (6%) and hazardous to the environment. Other pests include Folate (vitamin B9) 21 µg (5%) squash bugs ( Anasa tristis ), leaf miners ( Liriomyza sati- Vitamin B12 0.00 µg (0%) vae ), melon worm ( Diaphania hyalinata ) and whiteflies Vitamin C 36.7 mg (44%) Vitamin E 0.05 mg (0%) (Trialeurodes vaporariorum ). Please consult local Vitamin K 2.5 µg (2%) recommendations for effective pest control measures Ca 9 mg (1%) in your area (Cornell, 2004). Fe 0.21 mg (2%) Mg 12 mg (3%) Nutritional Values K 15 mg (2%) Zn 0.18 mg (2%) Netted melons are a good source of carbohydrate in the form of sugar. They are also a reasonably Percentages are relative to USDA recommendations for adults. good source of potassium and vitamin A (Table 10.4; USDA, 2011). known as citron, tsamma melon or preserving melon, is apparently native to the Kalahari Desert region as WATERMELON well. David Livingstone found extensive areas covered with wild watermelon vines in central Africa during Origin and History his explorations in the mid-1800s. Watermelons were The origin of watermelon is unclear but it was also cultivated in China as early as the end of the 9th cultivated at least as early as 2000 bc based on century ad (Zohary et al ., 2012). evidence from the Nile Valley (Zohary et al ., 2012). Watermelon was largely unknown in Mediter- Watermelon seeds were found in the tomb of ranean countries until introduction by the Moors Pharaoh Tutankhamen, as well as in other sites of in the 13th century. The word “watermelon” first the 12th Egyptian Dynasty, even though no litera- appeared in English dictionaries in the early 1600s ture or hieroglyphics depict or describe the eating (Mariani, 1994). Watermelons were apparently of watermelons. One theory is that watermelon introduced to North America in 1500s, because was derived from a perennial relative, C. colocyn- Native Americans were found cultivating them by this, which is endemic to Africa and was found in French explorers in the Mississippi valley. early archaeological sites before watermelon (Zohary et al ., 2012). However, some believe that Botany and Life Cycle watermelon was domesticated in Africa from puta- tive wild forms of C. lanatus. The Kalahari Desert Watermelon is in the family Cucurbitaceae (Gourd in south central Africa is a region where wild forms Family) and the genus and species are Citullus lanatus are still found, some of which do not have bitter (Thunb.) Matsum & Nakai, having formerly been fruit. The related species, C. lanatus var. citroides, classified as C. vulgaris or C. citrullus L. Watermelons

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Welbaum_Ch10.indd 30 8/4/2014 4:07:46 PM Types and Cultivars are annual with monoecious sex expression although some andromonoecious forms exist. The long-trailing Watermelon fruit vary in size, shape, flesh color stems or vines may exceed 5–6 m (16–20 ft) in length and surface color among cultivars (Fig. 10.17). and short internode “bush” cultivars require less Sizes range from 1 to 3 kg (2.2–5.5 lb) for small- space. Stems are thin, angular, grooved and hairy, fruited cultivars, sometimes referred to as “icebox” with branched tendrils that anchor the vines. Root or “midget”, to more than 24 kg (55 lb) for large- systems are extensive, deeper than some other cucur- fruited types. Fruits of some cultivars, like ‘Tom bits, although still relatively shallow compared to Watson’, may weigh as much to 60 kg (132 lb). Most deeply rooted crops such as tomato. The majority of icebox cultivars are similar in size to cantaloupe and the roots are within 60 cm (24 in) of the surface most have a thin rind that is not well suited for (Rubatzky and Yamaguchi, 1997). long-distance shipping. Birds can also peck seeds Leaves are large, 5–20 cm (2–8 in) long, and through the thin rind of some small-fruited cultivars. deeply and prominently lobed. Solitary, yellow Icebox types are popular with home gardeners and flowers range in size from 2 to 5 cm (0.8–2 in) in in short-season areas because of their quick maturity. diameter and are open for only 1 day (Rubatzky Many commercial markets prefer fruit in the 15–25 and Yamaguchi, 1997). lb (7–11 kg) range, that are easier to handle and Relatively large flat, smooth watermelon seed refrigerate. Fruit shapes range from round, oblong may be colored white, tan, green, red or black and or elongated with blocky or relatively pointed ends. 10–15 seeds weigh about 1 g (0.04 oz) (Lorenz and The rind of mature fruit is usually smooth and can Maynard, 1988). Large-fruited cultivars may con- vary in thickness from less than 1 cm (0.4 in) to tain 500 seeds. The large cotyledons make up much 4 cm (1.6 in). Exterior rind colors range from black- of the seed volume. Watermelon seedlings like ish green to yellow with solid, striped or mottled other cucurbits are epigeal with the cotyledons coloring. Wax accumulation on the outer rind sur- becoming photosynthetic organs after germination. face increases with maturity. The seed are scattered Cotyledons are oblong in shape with an incon- and imbedded in the edible placental tissue and there spicuous epicotyl developing between them. is no central cavity.

Fig. 10.17. Diverse sizes, shapes and colors of watermelon fruit at the Taiwan Watermelon Festival.

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Welbaum_Ch10.indd 31 8/4/2014 4:07:47 PM Cultivars differ with regard to flesh texture, color and sugar content. The placental tissue of modern culitvars is sweet and watery. The flesh texture of some fruit is fairly stringy or fibrous, particularly when over ripe. Flesh colors range from red, orange, pink, yellow, to white (Rubatzky and Yamaguchi, 1997). Red flesh color is due to the pigment lycopene while yellow color mostly comes from β-carotene and xanthophylls (Maness et al ., 2003). The flavor and sugar content of yellow-fleshed and red-fleshed melons are usually the same. Occasionally, flesh bitterness occurs in some heirloom fruit due to the presence of cucurbi- tacins, but seldom in modern cultivars. Most modern cultivars have black seeds because some consumers think a fruit with white seeds is imma- ture. Black seeds make an attractive contrast with red or yellow flesh.

Usage Watermelons are grown primarily for the sweet juicy fruit pericarp tissue that is chilled and eaten as slices or chunks, added to fruit salads or juiced. The rind maybe preserved in vinegar as a sweet or brined pickled product. Some watermelon cultivars and Citrullus colocynthis, a related species, are grown exclusively for their abundant and large seeds that are roasted or boiled with flavorings Fig. 10.18. This small-fruited watermelon in Israel is grown for its edible seeds. such as licorice. In both Asia and the Middle East, roasted or boiled watermelon seeds are a popular snack food (Fig. 10.18). Production and Culture Some watermelons are used for livestock feed Watermelon is a warm-season, frost-sensitive crop and extracted juice is fermented into an alcoholic that requires a relatively long growing season from beverage. Watermelon fruit are an important source 75 to 120 days depending on the cultivar and envir- of water in some desert areas, during drought, or onment. The optimum day and night temperatures where drinking water is contaminated. are 32° and 20°C (90° and 68°F), respectively. Crop Citron is also called preserving melon and is a rotation helps control soil-borne diseases like distinct inedible flesh type of watermelon that Fusarium or nematodes. Plastic mulch, row covers or resembles small edible cultivars. ‘Green Citron’ low tunnels help increase soil and air temperatures in Citrullus lanatus var. citroides has a hard tough short-season areas. Some cultivars, like ‘Klondike’ rind that can be used for pickling or animal feed. and ‘Peacock’, are tolerant of low humidity, are bet- Citron melon flesh is white, light green or slightly ter suited for production in desert areas, and have pink but generally inedible due to its hard flesh moderate drought tolerance. F-1 hybrid cultivars are and bitterness. The seed color is greenish tan. more uniform, more productive and popular despite Citron melons grow wild in some sections of their extra cost, although open-pollinated cultivars North America and can be weeds in commercial are still widely grown commercially in many areas. watermelon fields. Citron watermelons should not be confused with the candied diced citron Site selection and field preparation that is an ingredient in fruitcake and made from the peel of Citrus paradisi , a tropical tree fruit Soil compaction restricts root growth, so friable, also called citron. deep and well-drained sandy loam or loam soils are

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Welbaum_Ch10.indd 32 8/4/2014 4:07:47 PM preferred for watermelon production. Watermelons matter decomposition, the nitrogen cycle and micro- are often grown on raised beds to improve drain- bial fixation. The ideal soil pH is between 6.0 and age and support plasticulture production. Beds are 6.5 although a range from 5 to 7 is acceptable. formed so they are 15–20 cm (6–8 in) above the Fertilizer, as liquid or granular, is commonly applied bottom of the adjacent furrow. Final spacing of the as twin bands 15 cm (6 in) deep and 10–15 cm (4–6 in) beds is generally 203 cm (80 in) center-to-center to either side of the seed lines before planting, at plant- although other bed sizes may also be used. ing, or in drip irrigation lines as part of a fertility pro- Watermelons can be grown without irrigation or gram. Banding of fertilizer near the seed is preferred mulch but this is not recommended for commercial over broadcasting since the rows are far apart mak- production because most areas experience water ing broadcast applications inefficient. Nitrogen is deficits sometime during the growing season that commonly applied as a side dressing or as fertigation, lower yields and reduce fruit quality. Watermelon is particularly when vines start to spread. Petiole is the often produced on plastic mulch for weed control, to most effective means of diagnosing the nutrient status warm soil in short-season areas, to preserve soil of the crop during the season. Sufficient values for N moisture and to reduce the leaching of fertilizer that in the petioles sampled from the sixth leaf from the occurs following heavy rainfall. Plasticulture can sig- growing tip during early fruit development range from nificantly increase watermelon yields. Establishment 5,000 to 7,500 ppm, P values range from 1,500 to is by direct seeding or plug transplanting, especially 2,500 and K values range from 3 to 5%. for seedless production, through holes punched or The goal for optimized production is to grow burned in the plastic mulch. Drip irrigation or ferti- plants with a large canopy, while maintaining gation is used with plastic mulch to get sufficient healthy leaves as long as possible. This strategy water to the seed and root zone. Watermelon pro- maximizes the photosynthetic capacity of the plant, duction with conservation tillage is technically feas- which maximizes yield potential and fruit sugar ible but not widely practiced in North America. content. Canopy development and health is aided by maintaining sufficient levels of N, P, K, S, Ca, Mg, B, Cu, Fe, Mn, Mo and Zn throughout the Fertilizer and nutrition growing season. Watermelons should not be over- Watermelons tend to develop extensive root sys- fertilized especially with N. Excessive N increases tems in the upper profile of the soil allowing production costs, may damage the environment by efficient extraction of nutrients. For this reason, leaching into the water table, and may inhibit fruit fertilizer requirements are moderate compared set and delay harvest. The N level must be low with many other vegetables. A fertility program enough at flowering that the plant will form fewer should be developed with input from preplant soil new leaves once fruit development begins. This tests and foliar analysis during the season. Nitrogen allows more sugars to accumulate in the fruit, is the most commonly required fertilizer, although rather than being used for new vegetative growth. P is sometimes needed to promote seedling growth and maximum productivity and fruit quality. Field establishment Potassium increases rind thickness and cracking resistance and fertilization is often needed on lighter Seeded watermelon cultivars are often direct-seeded soils. A watermelon crop will remove approximately in warm-season areas. Seedless watermelons are 196, 28 and 196 kg/ha (175, 25 and 175 lb/acre) of transplanted from plugs because they germinate N, P and K, respectively, from the soil. General fer- poorly in the field under suboptimal conditions and tilizer recommendations for watermelon produc- seeds are very expensive. Bare-rooted watermelons tion range from 67 to 168, 45 to 168 and 112 to do not survive well in the field because they are 224 kg/ha (60–150, 40–150 and 100–200 lb/acre) sensitive to shock, so most are established with for N, P and K, respectively (Lorenz and Maynard, plug transplants. However, both seeded and seed- 1988). The actual fertilization requirement depends less cultivars are often transplanted in short-season on soil test results and plant utilization during the areas. Watermelon transplant scions may be grafted season. The difference between the amount applied on to squash or gourd rootstocks to increase and the actual crop need is due to leaching losses resistance to soil-borne diseases and nematodes, for N and K, soil binding which renders a portion improve drought resistance or enhance plant of the P unavailable, and N gained from organic growth (Fig. 10.19).

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Welbaum_Ch10.indd 33 8/4/2014 4:07:47 PM (a) (b)

Fig. 10.19. Simple machines can joint rootstocks and scions to make a successful graft union and reduce labor (a). A watermelon seedling grafted just above the cotyledons by removing the apical meristem of the rootstock and replacing it with a scion of a production cultivar (b).

Grafting has long been used as a disease control produces smaller fruit and wider spacing larger fruit. strategy for greenhouse production of cucurbits and Plant populations can range from 3,200 to 8,000/ha in the Middle East and parts of Asia where acreages (1,296–3,239/acre) (Lorenz and Maynard, 1988). are relatively small. With greater emphasis on sus- Vines are sometimes trained toward row centers to tainable production using fewer synthetic chemicals facilitate cultivation and harvesting. and decreased availability of soil fumigants, graft- ing of cucurbits is rapidly gaining popularity in Flowering and pollination other countries as well. The use of machines to aid the grafting process reduces labor. Watermelon is “day neutral” and flowers when plants Watermelon seeds are planted 2–4 cm (0.8–1.6 in) are sufficiently large. Most commercial watermelon deep. Most cultivars have a germination optimum cultivars have monoecious sex expression producing between 25 and 35°C (77° and 95°F), which will result separate male and female flowers on a plant. The in emergence in less than 1 week, but between 12° and most effective pollinators are bees. Hundreds of pol- 20°C (54–68°F) germination is slow and erratic and len grains must be equally deposited on all lobes of may require 2 weeks or more depending on seed vigor. the stigma of each female flower to ensure set and full Seed fungicide treatments are recommended to control fruit development. Environmental and disease factors damping-off disease, especially when planting into can significantly influence flowering, pollination and cool wet soils (Lorenz and Maynard, 1988). fruit set. Plants under stress will have fewer flowers Watermelon vines spread rapidly once established and will not set as many fruit as healthy plants. Rain, so wide spacing is typical for watermelon production strong winds and high or low temperature extremes (Fig. 10.20). Except for brush-type cultivars, spacing also will reduce bee activity, fruit set and yields. To ranges from 2.5 to 5.0 cm (1–2 in) in-row and from transfer sufficient pollen, about ten bee visits are 2 to 3 m (6.5–10 ft) between rows. Seeds can also be required on the day the flower is open. If pollination planted in hills rather than rows. Hills of three or is inadequate or if fruit load is excessive, flowers will four seeds can be planted at equidistant spacing 2–3 m abort. Poorly pollinated fruit may sometimes set but (6.5–10 ft) apart. Cultivars with long vines require are often misshapen. wide row spacing and are susceptible to wind If pollination is successful, the ovary of the damage. Short internode or bush-type cultivars can female flowers will enlarge rapidly. Early devel- be spaced closer at half the distance of vining culti- oping fruit have an inhibitory influence on the vars. Fields may be seeded at higher density to ensure development of late-formed fruit. Most vines of a good stand before thinning to a final spacing at the large-fruited cultivars can only support two or two- to four-leaf stage. Closer spacing generally three fruit at a time and female flowers forming

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Welbaum_Ch10.indd 34 8/4/2014 4:07:50 PM Fig. 10.20. Watermelon production field with full vine cover and developing fruit.

after fruit set will abort. Fruit thinning is some- When performing the 4n × 2n cross, pistillate times practiced to improve the size and sugar accu- flowers of the 4n plant are pollinated with 2n pollen. mulation of remaining fruit. Small-fruited cultivars Fertilization produces fruit with 3n seeds that are may support more fruit per vine. planted for seedless crop production. Fruits of The bee population needed to maintain that fre- watermelon are seedless because they are triploid quency of flower visitations is normally four to five and normally sterile so fertilization does not occur. strong colonies per hectare (1–2/acre). Placement On the rare occasions that fertilization does occur, of bee colonies within a field rather than along the the embryo usually aborts. Small, aborted seeds may periphery may double the flower visitation fre- be found in the placental tissue of seedless fruit, but quency with the same number of colonies. Good they are soft with no embryo, and can be eaten like cooperation between the grower and beekeeper is the seeds in an immature cucumber. essential for making sure the bees are present in Pollination is still required with a diploid cultivar time for flowering and to minimize bee kill from to stimulate ovary growth for parthenocarpic fruit insecticide applications if used. development. About 12–18% of the field must be interplanted with a diploid cultivar that serves as a pollen source for the seedless triploid cultivar. Seedless watermelon Sometimes a standard diploid cultivar is planted to Kihara (1951) first developed seedless watermelons pollinate two to four rows of triploid plants. When in Japan during the early 1950s. Tetraploid (4n) this approach is used, a pollinator cultivar should be and diploid (2n) plants are crossed to produce trip- of a contrasting color or shape to distinguish the seed- loid (3n) seed (Kihara, 1951). Diploid watermelons less fruit from the selfed diploid that are sold as seeded are treated with colchicine, a natural product from watermelon. Recently, diploid pollinator lines that autumn crocus that doubles the chromosome only produce male flowers have been developed for number, to create tetraploid plants (Deppe, 1993). seedless watermelon production (Freeman et al ., 2007).

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Welbaum_Ch10.indd 35 8/4/2014 4:07:51 PM Since the male pollinator only produces staminate Mexico are furrow irrigated but this traditional flowers, fewer plants are required for adequate pol- inexpensive system uses water inefficiently and lination. These pollinator lines make seedless pro- may lead to salt accumulation in soil. duction more efficient because a portion of the field does not need to be devoted to a lower-value seeded Harvesting and marketing fruit pollinator cultivar. The chromosome imbalance caused by triploidy Cultivars differ greatly in their times to fruit maturity. does not significantly affect plant or fruit develop- Some small-fruited cultivars mature 75 days after ment. Early seedless cultivars had a higher per- planting while others may require 140 days or centage of fruit defects such as triangular shape, longer depending on the environment. Ideally, fruit large blossom scars, hollow heart, light flesh color, are harvested when the sugar concentration is highest. off flavors and delayed maturity. However, modern Sugar is the primary determinate of quality along seedless cultivars have higher quality and greater with flesh texture. There are no other well-defined uniformity with few if any defects. flavor components other than sugar. Soluble solids Because triploid seeds germinate poorly, particu- (sugar) readings should be taken from the center larly at low temperatures, the seeds are more expen- because sugars are not always evenly distributed sive and seedlings are not vigorous, seedless fields are within the fruit. Higher sugar accumulation often often established by plug transplants to minimize occurs on the side of the fruit facing the sun away shock. Seedless transplants are often germinated at a from the ground. Soluble solids of 12% to more high temperature (32°C, 90°F) and the temperature is than 13% can be achieved by some cultivars. Fruits then lowered to 22–23°C (72–73°F) for seedling with less than 7% soluble solids generally do not growth. The coats of triploid seed tend to adhere to have good flavor. Fruit maturing when daily mean the seed coats of emerging cotyledons, which can dis- air temperatures are below 21°C (70°F) has poor tort and cause poorly developed seedlings. Orienting quality. Sugar content does not increase after har- seed with the radicle end up when planted may help vest. Watermelon do not ripen once harvested so it seedlings lose their coats during emergence. is important to allow fruits to fully mature on the vine to achieve their maximum sugar content. Watermelons do not abscise from the vine when Irrigation ripe like cantaloupe. In commercial fields, har- Despite the fact that watermelon has an extensive vesting crews determine maturity by examining the root system, a consistent supply of water particu- color of the fruit’s ground spot. The ground spot is larly during fruit development maximizes both white where the fruit rests on the soil and the rind yield and fruit quality. Preplant or post-plant irri- does not develop chlorophyll. As the melon ripens, gations will ensure rapid seed germination, emer- the ground spot changes from white to pale yellow. gence and stand establishment. Irrigation is often When the fruit is ready for harvest the ground spot applied sparingly until the pre-vining stage to avoid will be pale yellow, and will turn dark yellow when cooling the soil, inhibit damping-off diseases, and overly ripe (Fig. 10.21). encourage deep-root formation. Watermelon crops The ground spot color of ripe fruit varies some- require from 400 to 700 mm (16–28 in) of rainfall what with cultivar. Also during ripening the color of or irrigation for maximum productivity. The gen- the rind will fade from glossy to dull green and the eral recommendation for at least 2.5 cm (1 in) tendril dies at the node where the fruit is attached to water/week either from rain, irrigation or both the vine. These are the most reliable indications of applies and more water is required on sandy soils maturity. Tapping or thumping to hear a dull sound or when mulch is not used. is subjective and not a reliable method for deter- Drip irrigation, either with or without the use of mining fruit maturity. A dull sound may be the result plastic mulch, conserves water and provides uni- of “hollow heart”, a common disorder that occurs form application directly to the root zone at a slow when an open space forms in the fruit tissue. Soluble rate. Sprinkler irrigation is often used for stand solids measurements or tasting, although destructive, establishment, but this is not the best system once are the best ways to evaluate fruit maturity and the vine canopy has developed because it may quality. When sampled fruit are sufficiently ripe, it is increase vine and fruit disease. Level production assumed that fruit of similar size and age in the same fields in the southwestern USA, western USA and field are of equivalent maturity and ready for harvest.

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Welbaum_Ch10.indd 36 8/4/2014 4:07:51 PM Fruit tissue becomes “grainy” around the seed when Fruit are most turgid and susceptible to cracking dur- overripe. Delayed harvest or prolonged storage ing early morning hours. Flesh firmness and rind causes the flesh texture to become mealy and stringy toughness are important cultivar characteristics for as cells collapse when over mature. shipping without damage. To maintain harvest quality, fruit should be quickly cooled and stored at 13–16°C (55–61°F). Watermelons are not suited to long-term Postharvest handling storage, but can be held at 80% RH for 2–3 weeks Fruit should be cleanly cut at the stem end rather than with little loss of quality if optimum temperatures are pulled from the vine. Fruit rinds may give the appear- maintained. Extended storage at 10°C (50°F) or less ance of strength but actually are susceptible to crack- results in quality loss due to chilling injury. The waxy ing from compression or impact shock and should not rind limits desiccation. Watermelons are not climac- be stacked on the stem or blossom ends. Watermelons teric, and immature fruit cannot be ripened off the may be shipped in bulk or in cardboard or plastic pallets. vine with ethylene treatment. Watermelons should, Small-fruited cultivars can be packed in cardboard ideally, not be stored or transported together with cli- pallets to prevent fruit damage from compression. macteric fruit that give off ethylene at harvest such as apple, cantaloupe or tomato because ethylene will cause pitting of the skin, flesh breakdown and black rot, shortening the storage life. Sale of precut watermelons has increased dramat- ically in some markets. Precut-watermelons offer greater convenience and an appropriate quantity for single people and couples. Precut watermelons are sold ready-to-eat in resealable containers with the rind removed. Precutting reduces preparation time and waste that the consumer must deal with. Precut products also allow the consumer to evaluate the flesh color and texture prior to purchase. In Japan, watermelons are sometimes grown in square molds (Fig. 10.22a). Molded watermelons command a premium price and are often given as pre- sents for special occasions. Watermelons are also used Fig. 10.21. Observing the change of ground spot color for carving to make table decorations. Very complex from white to yellow is a reliable way of determining designs and figures can be sculpted using the different ripeness. colored layers of a watermelon fruit (Fig. 10.22b).

(a) (b)

Fig. 10.22. Watermelons can be molded into different shapes by placing rigid containers around the developing fruit (a). Watermelon fruit may become elaborate art objects when carved (b).

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Welbaum_Ch10.indd 37 8/4/2014 4:07:53 PM Diseases Acidovorax avenae subsp. citrulli. There are sev- eral symptoms, including leaf lesions and fruit A number of different diseases affect watermelon, spots that may cover the entire fruit surface in many of which are most prevalent under humid severe cases. Fruit blotch bacteria may eventually conditions. Damping off is favored by cold wet con- cause the fruit to rot and can be transferred by ditions and is caused by Phythium spp., Rhizoctonia infected seed, transplants or weeds (Lessl et al ., spp. or Fusarium spp. Damping off can infect seed- 2007). Another bacterium that may affect water- lings in the field as well as greenhouse transplants. melon is Xanthomonas cucurbitae, which causes Fungicide seed treatments and limiting moisture can bacterial pumpkin spot. Other significant water- effectively control damping off. Phytophthora root melon diseases include black root rot (Chalara and fruit rot ( Phytophthora capsici ) can infect elegans), fruit rot (Choanephora cucurbitarum), maturing fruit (Noh et al ., 2007). Gummy stem Alternaria leaf spot ( Alternaria alternata ) and blight ( Didymella bryoniae ) is a major fungal dis- cucumber blight (Alternaria cucumerina) (Zitter ease that can cause a numbering of disorders in et al ., 1996). watermelon fields or greenhouse transplants including damping off, crown rot, leaf spot, stem Insect Pests canker and fruit rot (Gusmini et al ., 2005). Gummy stem blight causes round or irregular, brown lesions Several species of cucumber beetle attack water- on the leaves and may also attack the stem causing melon, including Diabrotica undecimpunctata . elongated water-soaked areas that become gray. Both the beetles and larvae damage watermelon; Gum may ooze from the stem cracks and plant die- the beetles feed on the stems and foliage and lar- back is another identifying feature. vae feed on roots. Cucumber beetles are vectors Anthracnose (Glomerella cingulata var. orbicu- of bacterial wilt but watermelon is not as suscep- lare) attacks watermelon foliage and fruit. In severe tible to the disease as C. melo or C. sativum . In cases, leaves die back leaving only bare stems. India, the red pumpkin beetle ( Aulacophora Anthracnose is most common under warm rainy foveicollis ) is a significant pest, which feeds on conditions. the immature leaves and flowers. Epilachna bee- Downy mildew (Pseudoperonospora cubensis) tles ( Epilachna spp.) are common pests of water- occurs on watermelons worldwide and attacks the melon in Africa. The larvae and adults feed on foliage giving rise to yellow spots, which coalesce the leaves and chew holes in the stems and fruit into brown areas causing leaf curl and resulting (Cornell, 2004). in a scorched appearance of the crop. Powdery The melon aphid, A. gossypii, and the green mildew ( Sphaerotheca fuliginea and Erysiphe peach aphid, Myzus persicae, may infest water- cichoracearum) is a widespread watermelon foliage melon crops. Heavy aphid populations seriously disease (Tomason and Gibson, 2006). Fusarium weaken the plant and cause yellowing and wilting. wilt (Fusarium oxysporum) causes infected vines to Aphids also vector several viruses, which reduce wilt. In severe cases, the entire root system may plant growth and fruit quality. Several species of become brown and a soft rot may develop near thrips may also infect watermelon crops (Cornell, the crown. 2004). Watermelon is also susceptible to virus diseases Melon fruit fly (Bactrocera cucurbitae) is a pest that are often transmitted by aphids. Watermelon of watermelon in some countries. Adult flies lay mosaic virus causes leaf mottling and stunted eggs, which hatch into larvae within 1 week and plant growth. Other virus diseases that affect feed on the fruit, causing damage and also allowing watermelon include: cucumber green mottle mosaic, entry of fruit-rot pathogens. Watermelon crops cucumber mosaic, cucumber vein yellowing, cucurbit may be covered with netting to protect against fruit aphid-borne yellows, cucurbit chlorotic yellows, flies. Mites (Tetranychus urticae and related spe- squash leaf curl, squash mosaic, tomato spotted cies) are pests of watermelon, particularly when wilt, watermelon chlorotic stunt, watermelon silver conditions are warm and dry. Mites cause distor- mottle, zucchini yellow mosaic and cucurbit yellow tion of new growth and chlorotic spotting as well stunting disorder. as fine webbing on the foliage. Armyworms, some- Fruit blotch is a particularly devastating disease times referred to as melonworm or rindworms, throughout the world caused by the bacterium feed on the rind of developing fruit. There are

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Welbaum_Ch10.indd 38 8/4/2014 4:07:53 PM several types of armyworms that feed on water- Nutritional Values melon fruit including southern (Spodoptera erida- As the names suggests, watermelon consists mostly nia), beet (Spodoptera exigua) and fall ( Spodoptera of water (Table 10.5). Watermelon fruit also con- frugiperda) (Cornell, 2004). tain soluble sugar and significant concentrations of Seed corn maggots ( Delia platura , formerly some minerals. Lycopene, a pigment response for Hylemya platura) are a pest favored by early plant- red flesh color, is also an antioxidant. ing dates, heavy cover crops and cool-wet weather. Seed corn maggots attack a wide range of horticul- Table 10.5. Nutrient composition of watermelon fruit tural crops including beans, peas, cucumber, melon, tissue (USDA, 2011). onion, corn, pepper, potato and watermelon. Although these maggots feed primarily on decaying Nutrient Amount/100g edible portion organic matter, they will feed on seeds and seed- lings of watermelon and other crops. Similarly cut- Water (g) 92.6 Protein (g) 0.5 worms (Agrotis segetum and A. ipsilon) reduce Fat (g) 0.2 watermelon stands by feeding on young seedlings Carbohydrate (g) 6.4 (Cornell, 2004). Fiber (g) 0.3 Ca (mg) 0.7 Economic Importance and P (mg) 10 Fe (mg) 0.5 Production Statistics Na (mg) 1.0 According to the United Nations Food and K (mg) 100 Agricultural Organization (FAO), watermelon is Ascorbic acid (mg) 7.0 Vitamin A (IU) 590 the most widely grown cucurbit with an estimated Thiamine (mg) 0.03 3,413,750 ha (8,435,560 acres) worldwide in Riboflavin (mg) 0.03 2011 and production totaling 98,047,947 t of fruit Niacin (mg) 0.2 (FAO, 2011). An estimated 1,200 watermelon cul- tivars are grown in at least 96 countries. Asia leads the world in watermelon production with two- thirds of the volume, followed well behind by PUMPKINS AND SQUASH European (13%) and African (6%) production. Origin and History China, with 23% of the world’s watermelon pro- duction, provides most of the Asian volume. In The genus Cucurbita is believed to be native to 2009, China produced 65,002,319 t of watermelon tropical America. Archaeological evidence suggests on 1,776,579 ha (4,390,022 acres). Other major squash may have been first cultivated in producing countries were Turkey (3,810,210 t), Mesoamerica some 8,000 to 10,000 years ago Iran (3,074,580 t), the USA (1,819,890 t) and (Roush, 1997; Smith, 1997). Cucurbita pepo likely Egypt (1,500,000 t). originated in what is today the southwest USA and Watermelon consumption per person in the Mexico. Cucurbita argyrosperma may have origin- USA for 2011 was 6.8 kg (15 lb)/year. In the USA, ated in Central America and southern Mexico, per capita watermelon consumption has steadily while C. moschata may have developed further declined over the past 50 years likely due to com- south in Central America and northern South petition from a wide range of convenience- packaged America. Similarly, C. maxima apparently origin- beverages and frozen snacks. The per capita con- ated in central and southern regions of South sumption of watermelon remains highest in coun- America (Zeven and Zhukovsky, 1975). tries of the Middle East. In Egypt for example, Species of Cucurbita are among the most ancient consumption per person is nearly 45 kg (100 lb)/ crops cultivated in the Americas. The four species year. Of the watermelons used in the USA, 22% C. pepo , C. argyrosperma , C. moschata and were imported primarily from countries in Central C. maxima only exist in cultivation. The close rela- America. Texas produces the largest acreage of tionship with humans along with evidence of these watermelons in the USA followed by Florida, while species in the ruins of ancient American civiliza- California, Georgia and Arizona are other major tions, indicate their importance in the development producing states. of Native American agriculture. Squash was one

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Welbaum_Ch10.indd 39 8/4/2014 4:07:54 PM of the “Three Sisters”, maize (corn), beans and types including pumpkin, winter squash, summer squash, planted by Native Americans. squash, gourds; C. moschata Duch., which includes pumpkin and winter squash; C. maxima Duch., which includes pumpkin and winter squash; and Botany and Life Cycle C. argyrosperma Pang., which includes pumpkin, Cucurbita spp. are generally warm-season, frost- winter squash and gourds (Robinson and Decker- sensitive annuals, although Cucurbita foetidissima Walters, 1997). HBK is a perennial. Cucurbita foetidissima includes Summer squash are defined as fruits harvested in buffalo gourd, which has a variety of common an immature stage before the rind becomes hard names including calabazilla, chilicote, coyote (Fig. 10.23). gourd, fetid gourd, Missouri gourd, stinking gourd, Winter squash are physiologically mature fruit wild gourd and wild pumpkin. The buffalo gourd with a hard rind that cannot be penetrated with a is a xerophytic tuberous plant found in the south- fingernail, and contains viable seeds at harvest. western USA and northwestern Mexico. The fruit They can be stored for several months at room is eaten cooked like a squash when very young but temperature if properly cured and are free of mech- becomes too bitter for vegetable use at maturity. anical damage and disease. Pumpkin is another The buffalo gourd grows fast, requires little water, term for winter squash in much of the world. and produces a large massive underground tuber However, in North America pumpkins are essen- that has medicinal properties and has been pro- tially a winter squash with a bright orange rind and posed as a feedstock for biofuel production stringy flesh grown as a decoration for the fall fes- (Curtin et al ., 1997). The seeds can be used as food tival Halloween or made into pies. For Halloween and are high in both lipid and protein (Berry et al ., celebrations, orange or white mature pumpkin 1976). fruits of predominately C. pepo and C. maxima are Cucurbita ficifolia, known as Bouche, malabar decorated or carved (Fig. 10.24). or figleaf gourd, is a climbing vine that reaches Differences among the various species of from 5 to 15 m (16–49 ft) in length. The figleaf Cucurbita are subtle based on seed anatomy and gourd is a frost-sensitive annual in temperate cli- leaf and stem characteristics (Table 10.6). Although mates and a perennial in tropical zones (Andrés, leaf shape and surface marking can vary within a 1990). In nature, the figleaf gourd grows in moist species, a combination of stem, androecium, ped- regions at altitudes from 1,000 to 3,000 m (3,281– uncle, flesh texture and seed features is used to dif- 9,843 ft), but it can be cultivated in other climates ferentiate the species. Seed colors can be white, tan, because of its hardy root system and disease resist- ance. The figleaf gourd is used as a disease-resistant rootstalk for grafting to cucurbits that are suscep- tible to root disease. The flowers and tender shoots are used in Mexico as vegetables. The most nutri- tional part of C. ficifolia is its fat- and protein-rich seeds (Andrés, 1990). Other species of Cucurbita have been identified growing wild. These are not commercially important on an international scale, although they may be grown and consumed locally and may cross with other species. Three of the most significant species include C. lundelliana Bailey, which is native to Central America, C. andreana Millan, which is cross-fertile with C. maxima and is believed to be its wild progenitor from South America, and C. texana Gr. Millan, which is cross-fertile with C. pepo and Fig. 10.23. ‘Zucchini’, an example of a bush type summer native to southern USA and northern Mexico squash, grown on plastic mulch and drip irrigation in (Robinson and Decker-Walters, 1997). Nova Scotia. Fruits are classified as summer squash The primary species of economic importance because they are harvested when immature a few days include: C. pepo L., which includes many diverse after anthesis.

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Welbaum_Ch10.indd 40 8/4/2014 4:07:54 PM brown or black depending on the species. Examples of characteristics that differentiate the major culti- vated species of Curcurbita are listed in Table 10.6. The cutivated Cucurbita described in Table 10.6 are monoecious and most have long trailing vines and a prostrate growth habit unless supported. Certain summer squash cultivars of C. pepo have short internodes and a bush growth habit (Fig. 10.23). Taproots are moderate to deep with extensive shallow horizontal development. Flowers are bright yellow, borne singly in leaf axils, and seldom open for more than 1 day. Most Cucurbita species are day neutral, although in a few flowering is affected by day length.

Uses Cucurbita fruit may be very large, particularly fruit of C. maxima and C. argyrosperma. Large-fruited cultivars of C. maxima bred for exhibition have weighed greater than 800 kg (1,700 lb; Fig. 10.25). Cucurbita pepo is probably the most versatile and widely used species. Cultivars of both summer and winter squash exist in C. pepo. Some bush cul- tivars of squash are grown for their immature fruits Fig. 10.24. In parts of North America, pumpkin refers (summer squash, courgettes, vegetable marrow) or to orange cultivars of winter squash that are decor- ated or carved like this jack-o’-lantern to celebrate the at anthesis (baby squash) that are steamed, boiled, Halloween holiday on 31 October. A jack-o’-lantern baked or fried. The time-to-harvest for this stage of is a pumpkin whose insides have been removed and development depends on the environment and cul- replaced with a light or candle. tivar but generally ranges from 35 to 50 days.

Table 10.6. Characteristics that differentiate species of Curcurbita (Rubatzky and Yamaguchi, 1997).

Cucurbita species Leaves Fruit stems (peduncle) Seeds

C. pepo Prickly, deep sinuses Not noticeably flaring Tan colored between lobes or enlarged at Seed scar horizontal or attachment to fruit rounded C. moschata Not prickly, sinuses indistinct Distinctly five-sided, Color, grayish white to tan; or absent, lobes pointed; regularly grooved, hard margin thickened deeper in with rare exceptions, leaves Flaring at attachment to fruit color and different texture soft hairy, with white spots Roughly cylindrical, not from body of seed; seed at the intersections of veins definitely, irregular scar slanting, rounded or grooves, not flaring horizontal or noticeably enlarged at attachment to fruit; hard C. maxima Lobes rounded; rough hairy, Cylindrical, soft and spongy, Margin, when present, kidney shaped, white spots yielding readily to identical in color and never present thumbnail texture with body of seed; white or brown to bronze, seed scar slanting

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Welbaum_Ch10.indd 41 8/4/2014 4:07:54 PM Cucurbita pepo includes many cultivars of pumpkin and gourd that are widely used as orna- mentals. Gourds have distinctive shapes and color, but are not edible because of their very hard, thin rinds. Ornamental gourds of C. pepo with considerable variation in color and shape are also used as decorations to celebrate Halloween and Thanksgiving holidays in North America. The flesh of physiologically mature pumpkin and squash fruits may be boiled, steamed or baked for con- sumption (winter squash). The flesh may also be creamed, mixed with spices and eaten as a pudding or as pie filling. Pumpkin pies are traditionally made for fall and winter holidays in North America. While pumpkin pies are often made from small and medium-sized fruit of C. pepo or C. maxima some prefer using butternut squash ( C. moschata ) because they have less fiber, small seed cavity, mild flavor and intense orange color (Fig. 10.26). Some C. pepo cultivars such as ‘Lady Godiva’, ‘Streaker’, ‘Triple Treat’, ‘Eat All’, ‘Sweetnut’ and ‘Hull-less’ produce “naked seed”. The naked-seeded pumpkin was derived from natural mutants whose seed coats include all tissue layers, but secondary wall thickening is reduced in the outer tissues (epidermis, Fig. 10.25. Prize-winning C. maxima fruit in a large hypodermis and sclerenchyma). As mature hull-less pumpkin competition in Bradford, Ohio. The fruit in the seed dry, the outer tissues collapse, producing a thin background weighed 910 lb (413 kg). seed coat that can be eaten without decoating

Fig. 10.26. Butternut is a popular and distinctive winter squash type that has excellent qualities for making pies and baking.

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Welbaum_Ch10.indd 42 8/4/2014 4:07:55 PM (Stuart and Loy, 1983). Because the seed coat is are leading producers. Illinois has significant pro- formed from maternal tissue, cross-pollination of cessing industry for producing pumpkin pie filling and naked-seeded cultivars does not affect coat develop- other products totaling about 3,600 ha (8,000 acres) ment. Although the feature improves seed edibility, (Fig. 10.27). the characteristic makes seed more susceptible to Summer squash are grown throughout the USA mechanical damage and decay after planting. with Georgia, Florida and California being the ‘Spaghetti squash’ also called “vegetable spa- leading producers. ghetti” is another unique edible cultivar of C. pepo. After cooking, the edible pericarp tissue can be Nutritional Values divided into loose strands resembling spaghetti but with crisp texture different from pasta. Except for vitamin C, winter squash are generally more nutritious than summer squash (Table 10.7). Winter squash are a typically a good source of Economic Importance and carbohydrates and vitamin A. Production Statistics World production of pumpkin, squashes and Production and Culture gourds in 2009 was estimated at 22.1 million t Growth and development produced on 1.6 million ha (3,953,686 acres) (FAO, 2011). The greatest production was in Asia Winter and summer squash and pumpkins are (14.4 million t), with China being the leading pro- warm-season crops that are sensitive to cool tem- ducer (6.5 million t). Total production in Europe peratures and frost intolerant. Most cultivated was about 2.8 million t, with the Russian Cucurbita are well adapted for growth at temper- Federation, Ukraine, Italy and Spain as the top four atures from 18 to 30°C (64–86°F) and are dam- producers (FAO, 2011). Africa produced 1.9, aged by chilling at temperatures below 13°C South America 0.7 and North and Central America (55°F). Although most are day neutral, Cucurbita 1.4 million t, respectively. In North America, the spp. generally do not grow well in the wet tropics, USA is a significant producer with 0.7 million t. although certain forms of C. moschata are adapted Winter squash and pumpkin are grown primarily to tropical conditions. Summer squash production in the northern USA. Illinois, New Jersey, California, is more widely dispersed than winter squash Indiana, New York, Ohio, Michigan and Pennsylvania (Rubatzky and Yamaguchi, 1997).

Fig. 10.27. A pumpkin field windrowed for mechanical collection and processing into pumpkin pie filling.

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Welbaum_Ch10.indd 43 8/4/2014 4:07:56 PM Pumpkins and squash can be grown on a wide summer squash production. Clear or infrared range of moderately fertile and well-drained soils. transmitting IRT is used in northern areas to Peat and heavy clay soils are not recommended. increase soil temperatures especially for early Clay soils generally have poor aeration and season planting of summer squash (Fig. 10.28). restricted drainage, which inhibit root growth and Planting through mulch is by direct seeding or increase fruit rot. Maximum yields are achieved on occasionally transplanting through holes punched medium-textured soils with high water-holding or burned through the plastic. Drip irrigation or capacity. fertigation is used with plasticulture. A crop rotation cycle of several years between No-till pumpkin production works well and is planting members from the family Cucurbitaceae is rapidly gaining popularity. No-till pumpkins are recommended if pathogen populations are high direct seeded or transplanted when soil is suffi- and soils are not fumigated between crops. When ciently warm in the early summer directly into possible, grasses, corn or sorghum are good rota- killed cover-crop residue, such as small grain-straw tion crops. However, care must be taken that there mulch, which serves as a weed barrier, conserves are no carryover herbicide residues, which might moisture and keeps fruit clean. inhibit growth. Pumpkins and squash are sensitive Spacing depends on whether cultivars are bush or to acid conditions and salinity. A pH range from vining. Wide plant spacing accommodates spread- 6.5 to 7.5 is ideal for good growth and yields ing vine growth. Spacing within rows varies greatly (Rubatzky and Yamaguchi, 1997). depending on plant growth habit and the desired Seed are planted about 2.5 cm (1 in) deep in fruit size, number and yield. Thus, spacing from 50 heavy soils and about 5 cm (2 in) deep in sandy to 150 cm (20–59 in) in rows and from 2 to 3 m soils. Soil temperatures should be above the min- (6.6–9.8 ft) between rows is common. Wide spacing imum of 15°C (59°F) for seed germination and at enables intercropping cultivation, which is used 30–35°C (86–95°F) emergence can occur within 1 week for high vigor seeds. In some tropical areas, plants occasionally are propagated from cuttings (Rubatzky and Yamaguchi, 1997). Pumpkins and squash are sometimes transplanted from plug trays with a root ball intact in short-season areas. Plastic mulch is sometimes used for pumpkins and winter squash production primarily for weed control, to keep fruit clean and for moisture con- servation since earliness is not a big issue except for

Table 10.7. Nutritional composition of summer and winter squash (amount/100 g edible portion; USDA, 2011).

Nutrient Summer squash Winter squash

Water (%) 94 89 Energy (Kcal) 20 37 Protein (g) 1.2 1.5 Fat (g) 0.2 0.2 Carbohydrate (g) 4.4 8.8 Fiber (g) 0.6 1.4 Ca (mg) 20 31 P (mg) 35 32 Fe (mg) 0.5 0.6 Na (mg) 2 4 K (mg) 195 350 Ascorbic acid (mg) 14.8 12.3 Vitamin A (mg) 196 4,060 Fig. 10.28. A maturing pumpkin production field using black plastic mulch and drip irrigation.

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Welbaum_Ch10.indd 44 8/4/2014 4:07:57 PM with cucurbits in some areas. Pumpkins and squash Potassium should be applied in conjunction with can also be planted in “hills” of three to five seeds soil and foliar test results and can be made by row each spaced 2–3 m (6.6–9.8 ft) apart. Bush cultivars banding or through fertigation during the season. are spaced closer with populations as much as two Phosphorus fertilizer, as liquid or granular, is to three times greater than for vining cultivars. commonly injected in twin bands 10 cm (6 in) deep The large leaf area of Cucurbita results in high and 10–15 cm (4–6 in) to the side of a row before evapotranspiration. However, many cultivars are planting or as liquid by fertigation. Banding of fer- drought tolerant due to their moderately deep root tilizer near the seed is more efficient than broad- system and extensive horizontal root proliferation casting since the rows are very far apart with vining near the surface. Nevertheless, because of the high cultivars. moisture requirements of these crops, soils with high water-holding capacity supplied with at least 2.5 cm Flowering and pollination (1 in) of moisture per week during active periods of growth is needed. Vining Cucurbita crops require Squash and pumpkin have monoecious sex expres- from 500 to 900 mm (20–35 in) of water to produce sion with separate male and female flowers on the a high-yielding crop. Summer squash with less exten- same plant. Both kinds of flowers are open a single sive root systems are more easily stressed during day. Male flowers rapidly senesce and abscise the day periods of drought. after closing. If female flowers are successfully pollin- ated, the ovaries will rapidly develop into fruit, but if not they will slowly wither and senesce after a few Fertilizer and nutrition days. Most vines of large-fruited cultivars can only Since pumpkins and squash efficiently explore the support two or three developing fruit at a time and soil for water and available nutrients, fertilizer later flowers will fail to set. Small-fruited cultivars requirements are moderate compared to many other can support many developing fruit on a single vine. vegetable crops. A high yielding crop of winter The most effective pollinators are bees. Several squash will remove roughly 168N-28P-168K kg/ha hundred pollen grains must be deposited on the (150N-25P-150K lb/acre) from the soil depending pistil of each female flower to produce a fully on the cultivar, soil and environment (Lorenz and developed fruit of marketable size and uniform Maynard, 1988). A summer squash crop may shape. Full pollination requires 10–15 bee visits remove slightly less nutrients. Fertilizer should be during the 1 day the flower is open. The bee popu- applied in accordance with soil tests before planting lation needed to maintain that frequency of flower and foliar test during the season. Plant tissue ana- visitations is normally four to five strong colonies lysis of petioles is the most effective means of diag- per hectare (1–2/acre). Plants under stress will have nosing the nutrient status of the crop in the field. fewer flowers and will not set as many fruit as Nitrogen is the most commonly required fertil- healthy plants. Reduced photosynthetic capacity, izer, although P is sometimes needed to promote rain, strong winds and high or low temperature early-season growth particularly in cool soils, maxi- extremes also will reduce bee activity and conse- mize production and achieve high fruit quality, quently reduce yields. especially in alkaline soils. Nitrogen is applied as fertigation in response to tissue analysis or as two Growing giant pumpkins side-dressings, the first at the two- to four-leaf stage and the second at vine spread. Care must be taken In some parts of the world, the size of winter squash to not over-fertilize with N, particularly early in the and pumpkins is important especially when growing season prior to flowering and fruit set. Excessive N fruit for exhibition (Fig. 10.25). Growing giant favors vegetative growth over reproductive growth, pumpkins and squash also illustrates some of the which can inhibit fruit set. The N level must be low important principles of fruit development. The first enough by the time of flowering so that the plant step is to select a cultivar that has the genetic poten- will form fewer new leaves after fruit set and tial to grow large fruit such as C. maxima cv. growth begins. This allows more sugars to go to the Atlantic Giant. Cultural practices help fruit reach fruit, rather than excessive vegetative growth. their maximum genetic potential. Plants must be Some mineral soils contain adequate K, but defi- grown at extra wide spacing to reduce competition. ciencies are common on light or infertile soils. After the first fruit sets, all other developing fruit

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Welbaum_Ch10.indd 45 8/4/2014 4:07:57 PM and flowers should be removed to eliminate com- after anthesis with the flower corolla still attached. peting “sinks” that draw photosynthetic resources Other markets prefer larger fruit (Fig. 10.29). from the single selected exhibition fruit. Minimizing It is important to harvest summer squash regu- disease and insect attacks on the plant is important larly to maximize plant productivity because larger because these stresses reduce photosynthetic cap- developing fruit tend to suppress the development acity. Plants should be watered regularly to optimize of new pistillate flowers. In some markets, clusters expansive growth and eliminate water stress that of open male flowers are harvested and sold as a would reduce photosynthesis by causing stomatal delicacy (Fig. 10.30). The flowers are prepared by closure. Plants should be fertilized weekly with a cooking in a number of different ways, usually complete analysis fertilizer after the fruit has set to with ingredients like eggs, flour or meat. ensure that essential mineral nutrients are not limiting. Some pumpkin growers inject carbohy- drates into the stem with the hope that they will be absorbed, translocated into the fruit, and metabol- ized to supplement natural dry matter accumulation through photosynthesis. Rotating the developing fruit periodically will help prevent the development of a flat side but this is for cosmetic purposes and will not affect final size or weight.

Harvesting and marketing Summer squash, such as ‘Yellow Straight Neck’, ‘Zucchini’ and ‘Patty Pan’ are harvested as immature fruit often as soon as 40–50 days after planting. Summer squash should be harvested when fruits are immature and glossy in appearance before significant Fig. 10.29. A succession of developing fruit with seed development begins. Preferred size varies senescing flowers on a bush green zucchini summer among markets. Some summer squash are harvested squash plant. Flowers are only open for a single day very early in their development, often just a few days and then rapidly senesce.

Fig. 10.30. Squash flowers for sale at a farmers’ market in Hania, Crete, Greece.

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Welbaum_Ch10.indd 46 8/4/2014 4:07:58 PM The development of most pumpkins and winter Diseases squash cultivars falls in the range of 80–150 days Anthracnose ( Colletotrichum orbiculare ) is a although the exact time is very cultivar and envir- destructive disease that causes defoliation and onmental dependent. Pumpkins and winter lesions on the fruits. Angular leaf spot ( Pseudomonas squashes should fully mature before harvesting. syringae pv. Lachrymans ) is caused by a bacterial Essentially, all Cucurbita fruit are hand harvested, pathogen. The bacterium can attack leaves, stems and except for summer squash, rind hardness is and fruit. Leaf symptoms begin as small, water- a usual indication of maturity sometimes accom- soaked lesions that expand to fill the area between panied by vine senescence. Fruits for storage veins, giving an angular appearance (Cornell, 2004). should be harvested after the skin is sufficiently Powdery mildew ( Erysiphe cichoracearum ), downy hard that a fingernail or similarly sharp object can- mildew ( Peronospora cubensis ), scab ( Cladosporium not penetrate it. When ready for harvest, fruit are cucumerinum ) and leaf-spot ( Alternaria cucumer- carefully cut off the vine with a sharp knife to min- ina ) primarily affect leaves and stems (Fig. 10.31). imize peduncle injury, a possible site for disease The same fungus, Didymella bryonia , that causes entry. Pumpkins for ornamental display are usually gummy stem blight in other cucurbits causes black cut well above the fruit attachment point so the rot (Cornell, 2004). Black rot is the fruit-infecting large stem can act as a fruit handle for carrying. Crop phase of the disease, and is most common on yields for winter squash range from 20 to 30 t/ha butternut squash and pumpkins, while gummy stem (9–14 ton/acre) (Lorenz and Maynard, 1988). blight refers to the foliar and stem-infecting phase Harvesting of bush cultivars of summer squashes of the disease. Choanephora wet rot ( Choanephora is complicated by short internodes that cause fruits to cucurbitarum ) causes a soft rot of squash fruit. be closely spaced, which interferes with removal. Serious virus diseases include: cucumber mosaic Fruits are harvested by cutting with clippers or a cucumovirus (CMV), watermelon mosaic 2 potyvi- sharp knife or by twisting the soft pedicle or fruit rus (WMV-2), watermelon mosaic 1 potyvirus, zuc- stem, by hand. Having soft skins, the fruit are easily chini yellow mosaic potyvirus (ZYMV) and squash scratched by the stiff foliar trichomes on the leaf peti- leaf curl bigeminivirus (SLCV). Damping off is oles and are very susceptible to physical damage and favored by cold wet conditions and is caused by rapid moisture loss. Summer squash are sometimes Phythium spp., Rhizoctonia spp. or Fusarium spp., sold in plastic-wrapped trays to protect fruit. Care and can infect seedlings and transplants in the must be taken to protect the harvester’s arms and field or greenhouse if disease-free media is not hands from abrasion by foliar trichomes as well. used. Phytophthora blight, caused by the fungal-like Crop yields for summer squash range from 7 to 15 t/ha organism Phytophthora capsici , causes a sudden wilt (3–7 ton/acre). Summer squash has a marketable of infected plants and/or white yeast-like growth on shelf life of only about 7–10 days at 13°C (55°F) and affected fruit. Fusarium wilt and crown rot are dis- is chilling sensitive and should not be stored at lower eases caused by several different members of the temperatures (Cantwell and Suslow, 2013). genus Fusarium , which has many subspecies that are Rough handling damages pumpkins and winter host-specific (Cornell, 2004). Fusarium species can squash despite their relatively hard rind. Fruit should be seed-borne, but also persist in the soil as spores for not be exposed to bright sunlight or hard freezes. After many years with no host. The spread of this pathogen harvest, winter squash are often cured at temperatures often occurs through movement of infested soil and/ between 27 and 30°C (81–86°F) at 80% RH for or plant debris. Bacterial wilt is not as serious a about 10 days to heal wounds that occurred during problem with pumpkin and squash as with cucumber harvest. Curing helps increase storage life by healing and muskmelon because the vascular elements are (suberize) cuts and bruises thus inhibiting entry of dis- larger and less susceptible to clogging. Still, this dis- ease pathogens that cause fruit rot. Undamaged or ease, which is spread by cucumber beetles, has been cured, disease-free winter squash and pumpkins can reported in Cucurbita and appears cultivar specific. be stored for several months at 13–15°C (55–59°F) and 55–60% RH depending on the genotype. Squash Insect Pests are chilling sensitive and should not be stored below 13°C (55°F), which can cause off flavors and rapid Squash vine borer is a major pest. This insect bores deterioration, particularly when fruit are returned to small holes that are visible on the outside of the room temperature (Cantwell and Suslow, 2013). stem to access the interior where if feeds and lives.

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Welbaum_Ch10.indd 47 8/4/2014 4:07:58 PM Fig. 10.31. Powdery mildew on squash leaves.

The debris surrounding each hole looks as References though the stem had been drilled with a small- Andrés, T.C. (1990) Biosystematics, theories on the diameter bit. Once inside the stem the borers are origin and breeding potential of Cucurbita ficifolia. In: sheltered and difficult to control by conventional Bates, D.M., Robinson, R.W. and Jeffrey, C. (eds) means. Biology and Utilization of the Cucurbitaceae. Cornell Cucumber beetles feed on flowers and young University Press, Ithaca, New York, pp. 102–199. seedlings causing mainly superficial damage. The Bélanger, R. and Labbe, C. (2002) Control of powdery leaf-feeding Epilachna beetles are a serious problem mildew without chemicals: prophylactic and biological for Cucurbita growers. The adult squash bug alternatives for horticultural crops. In: Belanger, R.R., (Anasa tristis) is dark gray and about 5/8 in Bushnell, W.R., Dik, A.J. and Carver, T.L.W. (eds) The Powdery Mildews. A Comprehensive Treatise . The (16 mm) long and sucks sap from the leaves and American Phytopathological Society Press, St. Paul, stems. In severe cases, the leaf first wilts, turns Minnesota, pp. 256–267. black and dies. Squash bugs can also feed directly Berry, J., Weber, C., Dreher, M. and Bemis, W.E. (1976) and damage the fruit. Squash bugs live through the Chemical composition of Buffalo Gourd, a potential winter in protected areas both under debris in the food source. Journal of Food Science 41, 465–466. fields and in buildings and lay eggs on the under- Cantwell, M. and Suslow, T.V. (2013) Pumpkin and side of leaves in the spring and summer. Aphids, Winter Squash: Recommendations for Maintaining primarily A. gossypii , do not cause serious injury to Postharvest Quality. Available at: http://postharvest. cucurbits. Aphid feeding may distort leaves. ucdavis.edu/pfvegetable/PumpkinWinterSquash However, some species of aphids transmit virus dis- (accessed 18 November 2013). Chen, J.C., Chiu, M.C., Nie, R.L., Cordell, G.A. and Qiu, S.X. ease. Resistant cultivars provide the most reliable (2005) Cucurbitacins and cucurbitane glycosides: control of virus diseases. Other insects that may structures and biological activities. Natural Product affect Cucurbita spp. to varying degrees include Reports 22, 386–399. cutworms ( Agrotis segetum and A. ipsilon ), Cornell (2004) Cornell Pest Management Guidelines for leafminers ( Liriomyza sativae ) and rindworms Vegetables 2004. Available at: www.nysaes.cornell. (Spodoptera spp.). edu/recommends (accessed 31 December 2013).

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